# Humus Binding to STS Clay



## Diana Walstad (Aug 17, 2019)

For those concerned about humus release from soils, I have some exciting results. Recently, I watched an aquascaping tank setup sponsored by the Raleigh Aquarium Society. Demonstrator used STS (Safe T Sorb), a gravel-like clay. 

The advantages of STS became clear: inexpensive ($7 for 40 lb bag at Tractor Supply stores), attractive dark color and a high CEC for binding nutrients. More on this in your archives from 2012 https://www.plantedtank.net/forums/29-substrate/149589-oil-dry-safe-t-sorb.html

The demonstrator used STS as a pure substrate, but I suspected that STS might be equally useful for low-tech tanks. That is, it might make a better cap than gravel or sand over a soil underlayer. With its high CEC, it would capture and bind nutrients released from a freshly submerged soil. 

I set up two 2 gal tanks with a quart (4 cups) of organic potting soil in each. One tank had 2 cups of a gravel cap, the other 2 cups of an STS cap. The organic potting soil that I used had been sitting outside for a year and was nice and moist. Apparently, soil bacteria had been busy decomposing/composting it, resulting in an impressive amount of humus. 

While my original goal was to see the effect of STS on plant growth, the rampant STS binding of humus was far more interesting. Photos show tanks at setup and then at 8 days. The tank with STS cap consistently had less humus than the one with a gravel cap. 

Bottle test experiments confirmed what I was seeing in the tanks. Bottles with soil covered with STS showed less humus in water than those where the soil was covered with sand or gravel. I measured beneficial decreases in pH (7.6 to 6.8) and ammonia in the STS bottles, making the STS even more attractive.

Equally interesting, at least to me, was that nutrients can actually increase this humus binding. It is done via cation bridging. Photo from my soil textbook shows cation bridging. 

In another experiment with graduated cylinders, I found STS that was soaked overnight with either NaCl or CaCl2 (5,000 ppm of each cation) was able to clarify the water of added humus much faster than STS soaked in plain distilled water. Apparently, the positive charges of the Na+ and the Ca++ bridged the negatively charged STS clay and the negatively charged humus. Result: clay and humus came together and precipitated out of solution, thereby clarifying the water. 

Photos show STS results at start where I mixed the three STS soils with added humus and then after 3 hours. At 3 hours, the difference was readily apparent. STS that had not been exposed to cations was much more turbid. Calcium with its two positive charges formed a better bridge than sodium, which is what I predicted and what my textbook says.

Bottom line: STS will remove humus released from the soil underlayer better than a sand or gravel cover. Nutrients released by the soil will facilitate this binding. (I'll be writing an article eventually with all the gory details, but wanted to get this out now onto this forum.)


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## nothreat33 (Aug 5, 2019)

It's the great Diana Walstad! It's very exciting to be reading a recent post from you. Very interesting stuff can't wait to read the article.


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## minorhero (Mar 28, 2019)

This is really interesting and from my perspective fantastically well timed. I will be setting up my first soil substrate tank in the next month. I thought about using sts as a cap but had decided not to go that route for fear of not adequately capping the soil. So I am excited to use sts going forward, especially since the color should help to hide fish poop. 😉


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## Diana Walstad (Aug 17, 2019)

Thanks for your encouragement! I was beginning to think no one cared. 

A couple things I learned that might be useful as you set up tank. You don't need to wash the STS but once at most. Because the STS comes full of air and therefore lightweight and difficult to hold plants down, I would soak the STS in water briefly before setting up your tank. 

People talk about how STS makes water turbid, so they wash and wash and wash away all the fine particles, which is where the highest and good CEC is. Instead, be very gentle with pouring in water and then do a water change after the disruption of planting. The finer particles will settle out in normal tap water. Even when I shook up STS with water for my experiments, the water cleared up pretty well by the next day. 

I think that combining soil and STS should work very well, better than STS alone, better than soil alone. It will be interesting to hear what you think.

Here's photo of tank setup for the RAS club's demo by Mark Denaro with pure STS-- preceded by informative lecture on STS by Neil Frank, expert aquatic gardener.


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## Streetwise (May 24, 2019)

Great stuff! Thanks for sharing this.


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## Beachcruiser (Aug 13, 2019)

Thank you for the update!

Sounds like I really need to join that Raleigh club...


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## reddhawkk (Dec 28, 2011)

What would be your thoughts on using peat under an STS cap for a blackwater tank?


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## Diana Walstad (Aug 17, 2019)

I don't think an STS cap would give you what you want. The STS would absorb the humic acids and tannins that make up "Black Water." The virtue of STS (to me and many others) is that it removes these organic compounds, which show up as tea-colored water, black water, etc. For your tank, I would use the peat with a gravel covering.


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## JJ09 (Sep 11, 2014)

I use safe-t-sorb in all my tanks. I don't have dirt substrate underneath, just the STS. I did soak mine in water before putting it in the tank, with baking soda because I read elsewhere that the STS would absorb calcium out of the water so fast it would cause large pH swings at first. Do you have any input on that?


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## SwampGirl (Jan 12, 2017)

Wow! That picture of the two tanks side - by - side with the STS vs aquarium gravel has convinced me to do a modified version of this over my 30 Gallon long tank that I plan to set up next week. In addition to what you have taught us about the CEC ability to absorb the humus (and I assume this means we can accelerate the timeline with which we add livestock? Correct me if I am wrong about that) it looks very natural which is what I was desperately looking for. 

Here is my plan for the setup of the substrate:

To the bare glass I will add a thin layer of osmocote (is this overkill with soil?) and powdered bentonite clay. I will also add some mulm from an existing tank to jumpstart the cycle.

I will spread ~1.5" organic soil over that. (probably whatever i can get at the local organic garden center, sifted for large sticks) 

Then cap with STS mixed with a small amount of crushed coral to buffer the pH (I want neutral pH and hardness in this tank, not too acidic.) I will probably eventually add some leaf litter and small twigs and plant fibers to create an even more natural substrate. 

Perhaps I am overthinking it and all that is required is the STS over soil? If it matters, my intended inhabitants are a group of _Pseudomugil Gertrudae_ and either wild type _Neocaradina _shrimp or _Cambarellus Shufeldtii_ and I will be planting with mostly Valisneria and Cryptocoryne species. I am also intending on having some emergent plants growing from a slightly raised platform in the rear to emulate the marginal zone of a swamp or billabong. 

Thank you for your wealth of knowledge!


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## GrampsGrunge (Jun 18, 2012)

If I'm not mistaken, Osmokote+ has Copper in it's micro-nutrients mix You don't want any Copper in a shrimp tank.


And "thin coat" of Osmokote granules? How much is that? like covering one granule thick? That's way overkill.


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## SwampGirl (Jan 12, 2017)

Oh thank you I had not noticed copper in the ingredients but I will definitely not use that then. (though I have shrimp doing fine in tanks that had been previously dosed with osmocote plus root tabs) By "thin layer" I meant about a small scoop of granules, not an entire layer, that I'm sure would be overkill. I think I will just forego fertilizer at the startup completely and rely on the soil's nutrients.


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## GrampsGrunge (Jun 18, 2012)

SwampGirl said:


> Oh thank you I had not noticed copper in the ingredients but I will definitely not use that then. (though I have shrimp doing fine in tanks that had been previously dosed with osmocote plus root tabs) By "thin layer" I meant about a small scoop of granules, not an entire layer, that I'm sure would be overkill. I think I will just forego fertilizer at the startup completely and rely on the soil's nutrients.



I think Seachem's Flourish and Flourish Iron comes in a non copper micros formulas.


I would check their ingredients on their webpage to make certain.


Seachem's Iron fertilizers are also in an Iron Gluconate chelater instead of the more toxic ETDA chelating chemistry. I would use about 1/3rd of their recommended initial dosage if this does become a shrimp tank.


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## DaveKS (Apr 2, 2019)

Diana Walstad said:


> I don't think an STS cap would give you what you want. The STS would absorb the humic acids and tannins that make up "Black Water." The virtue of STS (to me and many others) is that it removes these organic compounds, which show up as tea-colored water, black water, etc. For your tank, I would use the peat with a gravel covering.


Any idea of how the acidic nature of soil will effect the clay of STS long term?

Also might be interesting to run same experiment with some smaller grained clay like this turface. Higher density and tighter pore structure logically would capture humic compounds even better.


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## Seattle_Aquarist (Jun 15, 2008)

Hi @Diana Walstad,

I have used Safe-t-Sorb for my tanks for over 7 years now with good success in both 'high tech' and 'low tech' applications. I don't mix the substrate, just use it by itself. Here are some pictures of my STS tanks.

First 10 gallon low tech 8-1-2012 [email protected]









Same tank 9-10-2012









2nd 10 gallon low tech set-up 8-13-2013; still no CO2; [email protected]









2nd 10 gallon low tech set-up 10-17-2013









75 gallon high tech 3-21-2014









Same 75 gallon high tech 6-26-2014


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## ipkiss (Aug 9, 2011)

Hi all! Is there a difference for our purposes in the variants available?

https://epminerals.com/products/safety-absorbent-and-safe-t-sorb

Thanks!


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## Diana Walstad (Aug 17, 2019)

JJ09 said:


> I use safe-t-sorb in all my tanks. I don't have dirt substrate underneath, just the STS. I did soak mine in water before putting it in the tank, with baking soda because I read elsewhere that the STS would absorb calcium out of the water so fast it would cause large pH swings at first. Do you have any input on that?


I'm not sure what STS is doing. My experiments (see my post on 9/8/2019) with soil capped with STS show STS increased acidity, but STS also increased the GH (indicator of Ca and/or Mg levels). 

Whatever.... Neutralizing the STS with baking soda before putting it in the tank makes perfect sense!


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## Diana Walstad (Aug 17, 2019)

ipkiss said:


> Hi all! Is there a difference for our purposes in the variants available?
> 
> https://epminerals.com/products/safety-absorbent-and-safe-t-sorb
> 
> Thanks!


I don't know. Pictures shows what was used for the demo and what Roy (Seattle Aquarist) here uses. In a quick search of Internet, there's lots of anecdotal stuff about using STS alone, but not combined with soil.


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## Diana Walstad (Aug 17, 2019)

DaveKS said:


> Any idea of how the acidic nature of soil will effect the clay of STS long term?
> 
> Also might be interesting to run same experiment with some smaller grained clay like this turface. Higher density and tighter pore structure logically would capture humic compounds even better.


I'm not sure that I would call soils themselves acidic. After a few weeks, their pH gravitates towards neutral (my book, Fig VIII-5, p. 130). Components by themselves--no cation coatings--can be acidic. STS clay is acidic, humic acids in water are acidic, but once they combine with cations, then they lose their negative charges/acidity.

Turface seems like a worthy possibility, but not my "turf." Feel free to do a bottle test by shaking up some turface with water containing humus. Then if you like, shake up another bottle with STS and humus. Have a control bottle containing sand or gravel combined with humus. 

Folks, these little experiments are not that hard. Photo show my humus stock solution produced by shaking up some old potting soil with tapwater and letting soil settle out overnight. Then, photo of a "bottle experiment" on kitchen table for the STS + soil stuff. (My old Ball canning jars came in very handy for this!)


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## Diana Walstad (Aug 17, 2019)

SwampGirl said:


> Wow! That picture of the two tanks side - by - side with the STS vs aquarium gravel has convinced me to do a modified version of this over my 30 Gallon long tank that I plan to set up next week. In addition to what you have taught us about the CEC ability to absorb the humus (and I assume this means we can accelerate the timeline with which we add livestock? Correct me if I am wrong about that) it looks very natural which is what I was desperately looking for.
> 
> Here is my plan for the setup of the substrate:
> 
> ...


I would try to keep it simple. STS over soil. If you have softwater, then I would add the crushed coral to the substrate.


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## Desert Pupfish (May 6, 2019)

I set up a 55g tank with a thin layer of peat based potting soil capped with ≈2" of STS. While the STS did lower the pH by a full point and the gH also, and absorbed the nutrients from the potting soil so that they didn't measure on tests, there were apparently enough nutrients in the STS to fuel a massive algae outbreak for 2 mos. (Didn't help that I had my lights on 8hrs/day to start) Even after lowering my lights to 5hrs/day, I battled various kinds of algae for 2 months. So while the sTS absorbed the humus enough to not measure on tests, it still was available to the algae, while my plants sulked. After 2 months I added a UV sterilizer & started dosing Excel-- which finally knocked down the algae enough for the plants to start thriving. The jungle val & red lotus seemed to be able to utilize all the stored substrate nutrients and grew like crazy, and other rooted plants like crypts, & sword have put out lots of roots, though most are still growing slowly. The stems (except H Sunset) didn't do much as they weren't able to utilize the substrate nutrients, and there were none in the water column. Once I started dosing Excel & low dose Thrive they started to improve.

It would be interesting to see how long this absorptive effect lasts, and if the STS looses it's cation exchange capacity over time. And if the structure breaks down. I washed mine obsessively, and it still creates a dense heavy cloud of clay when I pull up plants, etc. The clay dust cloud stays on the bottom and sinks back into the STS in 5-10 minutes, so it doesn't have a big effect on water clarity. Now if I top it off after replanting, etc I just use unwashed STS, and it behaves exactly the same way. 

Thanks for sharing these experiments--many of us use SafeTsorb and have wondered about this. Looking forward to learning more.


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## SwampGirl (Jan 12, 2017)

Desert Pupfish said:


> ....While the STS did lower the pH by a full point and the gH also, and absorbed the nutrients from the potting soil so that they didn't measure on tests, there were apparently enough nutrients in the STS to fuel a massive algae outbreak for 2 mos. (Didn't help that I had my lights on 8hrs/day to start) Even after lowering my lights to 5hrs/day, I battled various kinds of algae for 2 months. So while the sTS absorbed the humus enough to not measure on tests, it still was available to the algae, while my plants sulked. After 2 months I added a UV sterilizer & started dosing Excel-- which finally knocked down the algae enough for the plants to start thriving. The jungle val & red lotus seemed to be able to utilize all the stored substrate nutrients and grew like crazy, and other rooted plants like crypts, & sword have put out lots of roots, though most are still growing slowly. The stems (except H Sunset) didn't do much as they weren't able to utilize the substrate nutrients, and there were none in the water column. Once I started dosing Excel & low dose Thrive they started to improve.


Desert Pupfish, can I ask how heavily planted your tank was at the start? Were all the plants you mentioned present or were they added. Also you say that you did not use any water column fertilizers. I wonder if perhaps starting with dosing both substrate and water column as Tom Barr recommends would have contributed to fighting algae. Personally I am in favor of algae as long as is doesn't destroy the plants I want and usually IME healthy growing plants don't get covered in algae so growing algae is actually a plus to me as long as it also grows healthy plants. 



> I would try to keep it simple. STS over soil. If you have softwater, then I would add the crushed coral to the substrate.


That is definitely wise. I have neutral water so I will just start with STS and organic soil. 

Speaking of I drove 20 minutes to the closest Tractor Supply and they did not have any in stock despite their website saying they did and the clerk's own inventory system claiming they had 22 bags. Strange, and disappointing as it was a rather far drive away from anything else I had to do.


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## SingAlongWithTsing (Jun 11, 2015)

would we get the same benefits if we set up with STS as the bottom most layer, followed by soil, and finally capping with sand? this is how I have it in current set up and makes me wonder if the brown diatoms i have are actually humus


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## Seattle_Aquarist (Jun 15, 2008)

ipkiss said:


> Hi all! Is there a difference for our purposes in the variants available?
> 
> https://epminerals.com/products/safety-absorbent-and-safe-t-sorb
> 
> Thanks!


Hi ipkiss,

I believe the green bag is the 40# size and the red bag is the 50# size. I have not tried the small bag.


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## Desert Pupfish (May 6, 2019)

SwampGirl said:


> Desert Pupfish, can I ask how heavily planted your tank was at the start? Were all the plants you mentioned present or were they added. Also you say that you did not use any water column fertilizers. I wonder if perhaps starting with dosing both substrate and water column as Tom Barr recommends would have contributed to fighting algae. Personally I am in favor of algae as long as is doesn't destroy the plants I want and usually IME healthy growing plants don't get covered in algae so growing algae is actually a plus to me as long as it also grows healthy plants.


I started with crypt, bacopa. ludwigia, H. Sunset, java fern, H. difformis, & mermaid weed--thinking the faster growing stem plants would better soak up nutrients released into the water column by the soil & help combat the algae. What I didn't take into account was that the nutrients were all bound in the STS and not available to the stem plants, but the algae could utilize them and went berserk. In retrospect, I should've put in the jungle val, swords, red lotus etc immediately to start soaking up those nutrients bound in the STS substrate. And I should've been dosing the water column from the outset as well--as you, Tom Barr and others rightly suggest. Doing liquid Thrive & Excel has helped immensely. 

I'm less worried about the algae on the walls--except on the front & sides for visibility. I find it comparable to a garden without weeds--a lush weedy garden is just as healthy and a better habitat for wildlife than a highly manicured one. For me it's all about striking a balance between what's attractive, what's healthy for the inhabitants (otos, snails & shrimp gotta eat too) and what's feasible for me to maintain. I think I'm getting closer to finding that balance--but there are always lots of shifting variables in our glass boxes....


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## Diana Walstad (Aug 17, 2019)

SwampGirl said:


> Speaking of I drove 20 minutes to the closest Tractor Supply and they did not have any in stock despite their website saying they did and the clerk's own inventory system claiming they had 22 bags. Strange, and disappointing as it was a rather far drive away from anything else I had to do.


Sorry, to hear this. 

In looking at my experimental results yesterday, I am less enthusiastic about STS It doesn't appear to be so much better than a sand or gravel cap that one must jump over hoops to get it. Yes, it binds humus, but the potting soil I used was an old, weathered, damp one that had apparently accumulated a lot of humus from at least a year of decomposition. 

I set up another experiment with a newly purchased, fresh potting soil--two 1 gal bowls. Substrate didn't produce any humus so the STS cap is not showing any better results--so far--than a sand cap. Both bowls are doing fine. 

I still need to monitor plant growth.


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## minorhero (Mar 28, 2019)

Diana Walstad said:


> Sorry, to hear this.
> 
> In looking at my experimental results yesterday, I am less enthusiastic about STS It doesn't appear to be so much better than a sand or gravel cap that one must jump over hoops to get it. Yes, it binds humus, but the potting soil I used was an old, weathered, damp one that had apparently accumulated a lot of humus from at least a year of decomposition.
> 
> ...


Out of curiousity what soil did you use? A lot of folks look for miracle gro organic choice soil but its either been discontinued or extremely hard to find. Do you know of any other good soils that are national brands?

Good to know about sts not necessarily being better then sand. I am still leaning towards getting it for my own tank simply because its darker in color to better hide fish poop.


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## Diana Walstad (Aug 17, 2019)

minorhero said:


> Out of curiousity what soil did you use? A lot of folks look for miracle gro organic choice soil but its either been discontinued or extremely hard to find. Do you know of any other good soils that are national brands?


Thank you for asking! I serendipitously chose a Walmart Potting Soil ($3.93 for a 8 qts) shown in photo. Main virtue was low price and low nitrogen. I ignored the fact that it contained perlite balls and it wasn’t organic. The chemical fertilizers were advertised as “slow release.” That seems to be true as 2 weeks after setup, I’m measuring no nitrites or ammonia in water in either bowl. pH and GH are stable, no humus release. Plants seem to be doing okay. Photo of bowls at 2 weeks, one on right has STS/sand cap, the other pure sand cap. (I added a little sand to STS cap to better hold plants down.)

Here’s more details about this soil: 

Composed of compost, forest products, Sphagnum peat moss and perlite. Chemical fertilizers are ammonium phosphate, ammonium nitrate, potassium nitrate, potassium sulfate, calcium phosphate. Some of these chemicals were polymer-coated so that they would release slowly. Overall, the soil was one of relatively low fertility; the NPK ratio was only 0.023, 0.03, 0.06. [In contrast, the MGOC (Miracle Gro Organic Choice) that I used successfully for my shrimp bowls several years ago had an NPK of 0.10, 0.05, 0.05.) 

When I first started using potting soil 30 years ago, I didn’t discriminate brands, etc, just bought what was available. I’ve recommended using MGOC, because it worked well for me and was readily available at the time.

Apparently, there are standards for potting soils in some states, such as North Carolina. Thus, manufacturers just can’t throw just anything they want into the bag.

State Fertilizer Laws & Regulations, and Links to State Ag Websites


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## Diana Walstad (Aug 17, 2019)

*Acidity of STS Experiment*



JJ09 said:


> I use safe-t-sorb in all my tanks. I don't have dirt substrate underneath, just the STS. I did soak mine in water before putting it in the tank, with baking soda because I read elsewhere that the STS would absorb calcium out of the water so fast it would cause large pH swings at first. Do you have any input on that?


Yes, I do via a recent experiments. They show that STS is very acidic. I can see why people using 100% STS neutralize it with baking soda. What concerns me is that used with soil, that acidity--if not neutralized--could hurt the soil biology. 

I set up a bottle test experiment designed to show that an STS cap would capture ammonia in the water and the soil. So I soaked the STS/soil in a liquid fertilizer solution containing 15 ppm ammonia. Then, I changed water to remove the ammonia for my start on 8/22 (Photo). Two days later on 8/24, I measured notably less NH3 in jars with STS, just like I had predicted.

However, at about 12 days, the NH3 increased dramatically in STS jars to 5 ppm. The two sand jars showed no ammonia. I think the STS acidity created a "soil meltdown." Dying soil bacteria and other microbes--killed by the acidity-- released their ammonia into the water. (Not sure, though. Would have to repeat experiment with neutralized STS.)

Granted, my bottle tests don't reflect the tank situation where there's more oxygen and a greater volume of water over the STS. Some people treat the STS beforehand with baking soda. Probably not a bad idea.

Attached are pictures of the bottles and my measurements of the water.


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## Penta (Aug 27, 2015)

What about this pond soil I've found at my local store "Compo Sana teicherde" ? : https://www.bloomling.com/compo/potting-soil-for-ponds


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## ntdsc (Jul 24, 2019)

I think the safe-t sorb is good to mix in with the soil/clay that's dug down below the topsoil the safe-t sorb as you say, as it's more hygenic than dissolved clay, but will just remove some of my dirt mixture and add some safe-t sorb at the soil level to help with the hygiene of the soil/ also mixing in gravel with the soil for aeration of larger sized gravel but the gravel part is there for compaction and filtering. I also have a thin layer of regular sand near the top to filter out the soil.


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## Diana Walstad (Aug 17, 2019)

Penta said:


> What about this pond soil I've found at my local store "Compo Sana teicherde" ? : https://www.bloomling.com/compo/potting-soil-for-ponds


I see from the soil's website that there is not much information provided such as the NPK, the percentage of nitrogen, phosphate, potassium. Most USA potting soils have an NPK rating which gives you a quick and easy way to compare the fertility of soils. A nitrogen concentration of about 0.02 to 1 percent has worked fine for me.

Without NPK standardized information, I think you just have to hope for the best. You have to assume that your local store is selling a decent product for growing aquatic plants. There's so much variation in potting soils and other factors that affect plant growth, that I would be optimistic.


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## lenticular (Sep 3, 2019)

I think tropicas substrate is mostly (~70%) clay!

Sent from my ONEPLUS A5010 using Tapatalk


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## nothreat33 (Aug 5, 2019)

Could I soak STS clay in a container full of liquid Seachem nutrient products (separately) to produce clay particles packed with that nutrient?

My goal is to create a substrate very very high in nutrients that wouldn't leak out into the water column but could supply a root system for a very very long time for a closed bottle ecosystem experiment.


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## Diana Walstad (Aug 17, 2019)

*Loading STS with nutrients*

I don't see why it wouldn't work. Actually, I was thinking myself of soaking the STS in a fertilizer solution, washing it, and seeing how it behaves as a soil cover. I'm thinking that many of the cationic fertilizer nutrients (e.g., Ca++, Mg++, Fe++, NH3+, K+) just might replace the H+ (acidity) protons on the clay particles. The result would be an STS that was not only more fertile, but less acidic. Of course, this is just fanciful speculation. But it's a very intriguing idea! :smile2:


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## Desert Pupfish (May 6, 2019)

I did something similar when I started my dirted tank 3 months ago. I used the water from mineralizing a peat-based potting soil that had worm castings & bat guano it it to soak the STS after rinsing it. It seemed to work, because except when I was dosing with ammonia during the cycle, the water column never registered any measurable amounts of ammonia, nitrites, or nitrates. Because there were no measurable nutrients in the water column, the stem & floating plants I started with sulked, while I had massive blooms of one type of algae after another for 2 months. When I added vals, they took off like crazy and started taking over the tank. The crypt balansae didn't grow fast, but tellingly didn't melt, and when I had to move one it had developed a massive root system despite not much growth on top. And the half tiger lotus bulb put out tons of roots and exploded towards the surface. The amazon Hadi Pearl is putting out lots of new growth also.

In retrospect, having loaded up the substrate with nutrients I should've focused on the heavy root feeders at first, as well as dosed the water column so the stem & floating plants could outcompete the algae. 

My 7.8 pH tap water initially dropped about a degree to 6.8. Not sure if it would've dropped further had I not charged the STS with the potting soil water. A comparison of charged vs uncharged STS on pH, hardness & plant growth would be a great experiment.


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## nothreat33 (Aug 5, 2019)

I was looking into literature about how montmorillonite absorbs macronutrients and came across this paper. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.561.2734&rep=rep1&type=pdf

I wanted to see how effective it would be to soak it in liquid fertilizer. But After looking at the graph is doesn't seem to be very impressive. And while I didn't see how large or small his clay particles were, they were in a solution and I'm sure much much smaller than STS.


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## jeffkrol (Jun 5, 2013)

Cations and Cation Exchange Capacity - Tas | Fact Sheets | soilquality.org.au
Only thing "I believe" would be soak worthy is Calcium.. 

Translating field studies w/ aqueous is problematic though..

https://www.agvise.com/educational-articles/cec-and-holding-n-in-the-soil/



> .The ammonium ion (NH4+) has a positive charge allowing the soil, which has a negative charge, to hold the ammonium until it is converted to the nitrate form. Guess what? When nitrogen fertilizer has converted to nitrate form, a soil does not “hold” any nitrogen because they both have a negative charge. The nitrate anion is free to move with water in the soil profile. Where the water goes, the nitrogen will follow........ CEC will not tell you how much nitrogen the soil will “hold.” Ammonium based fertilizers convert quickly to nitrate N in the soil and the nitrate anion is negatively charged and will not be held on the soil which also has a negative charge.


to sort of bring this full circle.. Ca++ is the key (?) to binding humus to clay..
http://eagle-rock.org/index.php/Clay-humus_complex


> These aggregate structures are made ​​by combining Tonkolloiden calcium bridges formed with humic substances into humic topsoil. The resulting organo-mineral compounds are known as clay-humus complex, or lime-clay-humus complex.





> An ideally balanced soil CEC is calcium 60-75%, magnesium 6-12% (these two totaling 80%), 3-5% for potassium, trace elements and hydrogen. Calcium and magnesium are nutrients that act in opposition to each other, yet the plant needs both. The ideal ratio is about 7 parts calcium to one part magnesium. Our soils tend to be low in both nutrients, so adding dolomitic limestone with both calcium and magnesium is usually a good idea.



food for thought..


Just something to peruse. 647 pages..
https://archive.org/details/in.ernet.dli.2015.267880/page/n11


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## Diana Walstad (Aug 17, 2019)

nothreat33 said:


> I was looking into literature about how montmorillonite absorbs macronutrients and came across this paper. I wanted to see how effective it would be to soak it in liquid fertilizer. But After looking at the graph is doesn't seem to be very impressive.


This paper only deals with phosphate, which has a negative charge. One would not expect P to bind directly to clay particles, which also has a negative charge. I don't think this paper or the figure applies to the many nutrients that _do_ have positive charges.

Bump:


Desert Pupfish said:


> A comparison of charged vs uncharged STS on pH, hardness & plant growth would be a great experiment.


Inspiring! And thanks for the information.


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## nothreat33 (Aug 5, 2019)

In my digging around for information about phosphorus or phosphate and montmorilonite clay I came accross a few things that did mention it but I dont' have any good education to decipher these papers. 

Here's one paper

And this one.

And I saved some quotes that I thought might help me get to the bottom of it.



> Only initial phosphate concentration influences the degree to which a
> clay adsorbs phosphate, i.e. higher phosphate concentration resu Its in
> more adsorption.


From here: 
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.561.2734&rep=rep1&type=pdf

And:



> "The Al-modified Bentonite samples were prepared by mixing Bentonite with selected Al-solutions prepared with [OH]/[Al] ratios equal to 2.4. The dried Al-modified clay samples were ground and sieved to produce various sizes ranging between 63 µm to 425 µm. The adsorption results showed significant phosphorus removal enhancement with size reduction."


 From here: https://www.researchgate.net/public...fied_Bentonite_Clay_-_Effect_of_Particle_Size.

Does anyone know if STS Clay prefers one kind of cation over another? If I soak STS clay in Seachem Flourish Comprehensive with cations of:
NH4, K+, Ca2+, Mg2+, Mn2+, Zn2+, Cu2+, Fe2+, Na+

Would the clay have a "preference"? Would one cation be more successful and out compete other cations for spots to bind to?


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## Diana Walstad (Aug 17, 2019)

nothreat33 said:


> Does anyone know if STS Clay prefers one kind of cation over another? If I soak STS clay in Seachem Flourish Comprehensive with cations of:
> NH4, K+, Ca2+, Mg2+, Mn2+, Zn2+, Cu2+, Fe2+, Na+
> 
> Would the clay have a "preference"? Would one cation be more successful and out compete other cations for spots to bind to?


I _am sure_ there is a preference. Different cations have different sizes and strengths of their charge. That's why each element gets its own spot in the Periodic Table! 

Interestingly, I would have expected Ca++ to bind more tightly than K+, because Ca++ has more positive charges. My textbook*, however, reads, "Experimentally, it has been established that the strength of binding of K+ to montmorillonite is greater than that of Ca++, largely because the closer distance of approach of the monovalent ion (K+) is a more important factor than its lower charge." [Apparently, K+, can fit itself and squeeze into the little cavities and pores of clay better than Ca++. Moreover, NH4+ behaves similar to K+; both make a snugger fit than Ca++.]

However, I don't think these individual preferences matter that much. My questions are: Can I load up STS with plant nutrients that will replace the H+ cations that apparently are now bound to the STS and generating all that acidity in the presence of soil. Will fertilized STS react less with a soil underlayer than in my previous experiment, where the substrate seemed to have gone into a "meltdown" and released a ton of ammonia, increased the GH, and decreased the pH? 

Separate experiment, if I'm still interested, is: Will plants grow better with fertilized STS?

I am now soaking STS with a liquid Miracle Gro Garden general fertilizer that I use for gardening. In another bottle test, I'll compare it with unsoaked STS--with and without soil. 

*Wild A. 1988. Russell's Soil Conditions and Plant Growth (11th Edition). John Wiley & Sons (NY), page 248.


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## varanidguy (Sep 8, 2017)

Diana Walstad said:


> I _am sure_ there is a preference. Different cations have different sizes and strengths of their charge. That's why each element gets its own spot in the Periodic Table!
> 
> Interestingly, I would have expected Ca++ to bind more tightly than K+, because Ca++ has more positive charges. My textbook*, however, reads, "Experimentally, it has been established that the strength of binding of K+ to montmorillonite is greater than that of Ca++, largely because the closer distance of approach of the monovalent ion (K+) is a more important factor than its lower charge." [Apparently, K+, can fit itself and squeeze into the little cavities and pores of clay better than Ca++. Moreover, NH4+ behaves similar to K+; both make a snugger fit than Ca++.]
> 
> ...


Very interesting! I always wondered about using MG fertilizer for aquatic plants, but was also very nervous at the thought because the label states it's high in nitrogen and it uses mainly ammonium. I'm eagerly awaiting the results you have with this!


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## nothreat33 (Aug 5, 2019)

STS Clay may provide a way to add additional Nitrogen, Iron, Magnesium, and Potassium to new substrate to enhance it with nutrients that wont leach into the water. This would be done by soaking the clay in respective Seachem products or fertilizer of your choice.

An obvious problem though is calculating the strength of the charged clay.


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## Seattle_Aquarist (Jun 15, 2008)

Hi @Diana Walstad



> My questions are: Can I load up STS with plant nutrients that will replace the H+ cations that apparently are now bound to the STS and generating all that acidity in the presence of soil.


After I had been using using STS as a substrate on a couple of smaller tanks in 2014 I decided to use it for a new 75 gallon that I was setting up. Since our water here in metro Seattle is very soft (1.0 - 2.0 dKH / 2.0 - 3.0 dGH) I decided to try to 'pre-load' some nutrients into the substrate. *Here is the thread where I did a journal on APC.* I 'pre-loaded' the substrate with:


> Next I 'pre-loaded' the substrate by adding about 4 gallons of water to which I had added KNO3; KH2PO4; MgSO4; CaCl; and about 6 tablespoons of Seachem Equlibrium. After the substrate had soaked for about an hour I began the washing process. I put about 4# in a 4 gallon bucket and washed and rinsed the substrate about 4 times per batch. Then I dumped each batch in the 75 gallon and did a rough grade with it slightly deeper in back (about 2") and along the sides and more shallow in front (1.5").


I planted the tank on March 27th, 2014 and it looked like this:









This is what it looked like on May 9, 2014:









Here is what it looked like on June 26, 2014:









During that time I was dosing the 60 gallon water volume:
3X per week: 5/8 tsp. KNO3; 8/32 K2SO4; 6/32 tsp. KH2PO4; 6.0 ml Glut
3X per week: 6.0 ml. Flourish Comprehensive; 6.0 ml Iron; 6.0 ml CSM+B; 6.0 ml Glut
After 33% water change I would add 3 tsp Equilibrium

What I have also found in my STS tanks is I can go on a vacation of 10 days and not have to dose nutrients (I do cut back on the photoperiod) and the plants continue to grow without signs of adverse effects. Possibly due to nutrient retention in the substrate? ( I do have someone come in and feed the fish every other day).












Hi @Diana Wals









'


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## Diana Walstad (Aug 17, 2019)

Roy, your recipe for pre-loading the STS with calcium, magnesium, potassium is impressive. 

The avoidance of ammonia was smart. I gave up on soaking the STS with a dilute Miracle Grow fertilizer solution (15 ppm ammonia). I just could not wash out the ammonia from the STS enough to _even start_ an experiment. 

However, I do have results to report from the bowl experiment that I wrote about on my 9/2/19 post. Plant growth and water parameters are equally decent in both bowls. 

My results using STS in planted bowls gave much different (and better) results than those in the bottle jar tests (9/8/19 post). In bowls, I didn’t see much difference between using sand or STS as a soil cover. [I added a bit (~3/4 cup) of sand to the STS bowl to help hold plants down.] The KH, pH, and GH were about the same, plus no ammonia. 

Going forward, I’ll probably use STS since it’s so inexpensive and readily available here. Folks trying it out for the first time might want to monitor the KH and the pH for first few weeks. In hardwater situations, the KH lowering might be advantageous. In softwater situations, one can always add baking soda if KH and pH gets too low. Or use Roy’s recipe for pre-soaking with hardwater nutrients.

Photos show final test results and bowls at 2 days and 26 days. The bowl on the right is the one with the STS/sand cover. (Just now I see that the floating Frogbit has lost its green color. Probably an iron deficiency, so I may add some trace elements.) 

Factors that would explain the different results between bowls and jar are: 


The ratio of STS to water was 1:16 in bowls, but only 1:3 in jars. [Jars contained ½ cup of STS and 1.5 cups water compared to 1 cup STS in the 1 gal (16 cups) bowl.]

In jars, the STS depth was 1.5 inches (too deep!); in bowls about 0.5 inches. The jar’s thicker STS layer would make the soil more anaerobic. Also, in bowls, the substrate had a greater surface area, and thus, increased exposure to oxygenated water. 

In jars, I started with a much more fertile potting soil (NPK= 1.1%, 0.3%, and 0.35%). Moreover, I added a dilute liquid fertilizer (1/2 cup containing 15 ppm ammonia) to the potting soil (1/2 cup) in each jar. In contrast for the bowls, I used a different potting soil (2 cups/bowl) that had a much lower NPK (0.023%, 0.03%, 0.06%), and I did not add any fertilizer to it. 

The presence of plants would oxygenate the water and root area.


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## FlatfishTanker (Sep 17, 2019)

I'm coming into this discussion pretty late and am not sure if anybody is still following this. Admittedly, I have a hard time following all the scientific speak, and will not be attempting to add or modify anything with different fertilizer elements. So, in plain speak, is the reason we are excited to cap soil with STS because it better seals the nutrients into the soil and keeps it from entering the water column? Is that why, when people use an STS cap, they end up having to dose the water with more nutrients? Why not let some of the soil nutrients leach into the water so you don't have to add fertilizers back into the water? Is it more of a water clarity issue? I'm just trying to understand.

When I start my Walstad tank, is it best for me to just stick with the gravel cap and leave the STS to the experts? What about mixing STS and gravel about 50-50? Advantages of STS cap while letting SOME stuff through?

Wayne


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## DaveKS (Apr 2, 2019)

Most soil tanks leach to many compounds back into water column when 1st setup, usually you have to do some water changes at 1st till tank stabilizes at around 3-4mo in. This was her attempt at using STS (high CEC rating) to absorb and hold more of those nutrients in substrate. 

Seems little bowl on right with STS in her last post the water was a little clearer looking to me.


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## minorhero (Mar 28, 2019)

The original test was originally to clear up humus from the water column. It worked great but its less helpful for water clarity issues when humus was not such an overwhelming component of the soil she used. That said, sts has a high CEC value, meaning that it will store nutrients we add to our water and release it slowly over time. I am currently dry starting a walstad tank with sts and sand mixed together. I can't really advise doing sts just by itself simply because its a very light substrate. Even lighter then eco-complete. Mixing it with sand really helps hold the plants in place.


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