# Balancing tank to minimize algae



## willbldrco (Mar 24, 2007)

*Make as many changes as possible to drive to your goal*



naturelady said:


> My tank needs help!
> 
> I'm starting to get various kinds of algae growing and am looking to figure out some things to change to get the tank more into balance. By "various kinds," I mean most kinds... there are a couple of threads of hair algae, some brown diatoms, what I presume is green dust algae just starting on the glass, and some green, branchy, non-slimy stuff that I think might be cladophora. The algae is just starting, so I want to work to get the tank balanced before I end up with a huge problem.


It's good that you're addressing it quickly!



> I've had my tank set up for almost 6 weeks now and it is cycled. I have 2 guppies (and a few unwanted guplets), 6 habrosus cory cats, about a dozen cherry shrimp, and a bunch of unwanted snails. The fish were all added within the last 2 weeks.


With the fish, came the fish feedings, I'd wager. This means within the past two weeks you've started adding phosphates (via the fish food) and the fish have, the way they naturally doo-doo, been adding ammonia, which will be mobilized by your tank's nitrifying bacteria into nitrates. So your ferts have changed within the last two weeks due to the fish and feedings and it's probably trying to come to an equilibrium again.

I'd suggest an immediate 50% water change, re-dosing using the IE method - at 100% desired levels of ferts. This will take care of any water quality issues initially.



> CO2: DIY CO2 with a Hagan ladder that is really slow... ~16-18 bpm. I am borrowing this from a friend currently, so won't have it in a few months, and need to decide if I keep with the CO2 or not.
> Filtering: ~150 gph HOB filter.


This is a problem: Your CO2 is weak, then made worse by a filter which agitates the water (and I suspect is not sealed to prevent out-gassing). Your high KH and pH set you up to reduce disolved CO2 levels further. Check out the red line on this graph:










H2CO3 is carbonic acid, which is basically CO2 dissolved in water. That's the form of carbon your plants want and need. At 7.8 pH, you're stuck in an alkaline environment which reacts with dissolved CO2 to form bicarbonate (blue line) or carbonate (green line), both trap carbon in a form which your plants can't make use of during photosynthesis. In addition to that your hard water (high KH), is creating a buffering situation where the pH is more difficult to change. Even if you push lots of CO2 into the tank, with your high KH, much of it will become unavailable to the plants by reacting to form bicarobonate or carbonate.

I'd suggest trying to lower your pH by lowering your KH and increasing your CO2 rate, if possible - in fact, if you do just one, you will help drive pH in the direction you want it to go, and effectively increasing dissolved CO2 which is your holy grail. E.g, cutting your tap water with reverse osmosis water will reduce KH, making the pH easier to shift lower by your DIY CO2 injection. Increasing your flow rate of CO2 and addressing your filter out-gassing issues (seal it with plastic wrap), will drive CO2 concentrations higher, driving down your pH.

If possible, I would suggest working to do both these things, but if that's not possible, push for one and you will gain a little on the other, since they are related.



> Water parameters:
> Ammonia, nitrite, nitrate: all 0


Having your nitrates at 0 is bad. This suggests there is little to no nitrogen available to your plants. Perhaps this is a limiting factor in your fert levels (it's all been sucked up by the plants) or maybe it's a bad test result (I'd re-test it after a water change and IE dosing).

I didn't see a value for your phosphates. Do you have a kit for that?



> Plants:
> Anacharis currently growing back from melting
> Myriophyllum currently growing back from melting/being killed by hornwort
> Java moss
> ...


That's quite a mix! It will be interesting to see how the HC works out - usually it has high light needs. I'd make sure your floating plants are kept away from it to prevent shadows on the HC.



> The original goal was to be low-tech, thus the plants that do well in low light (and I love the anubias!). But I am guessing I will need some fast growers to out-compete the algae? Or more CO2? Or maybe take out the CO2, cut back on lights, find a whole bunch more patience (is hard!), and get back to the goal of being low tech?


The pH/CO2/KH relationship is the same in both high and low tech envs so my advice there should apply to either path you choose.



> I am not sure what the best option is. Suggestions? The goal is to eventually get a better light fixture and filter, but I need to work with the funds I have for now. Adding a lot more tech is not financially feasible for me right now.


Ah yes, money. Ugh! Wish we all had much more of it!  I'd do as much as possible with what you have. The problem I've found with planted tanks is that changing 1 or 2 things rarely works (unless you're tank looks fantastic and you're just tweaking a few things here and there). If you've got a zoo of algae, you've got to examine and fix all problems at once. In your case, I'd do ALL the following:

1) 50% water change ASAP; ferts via IE
2) Verify your nitrates have been fixed. If it's 0, add until it's at a good level.
3) Clean your filter
4) Do something to increase your dissolved CO2 - that means both increasing the flow, reducing surface agitation of the water, and sealing your tank and filter.
5) Reduce your KH. Once done, you should see your pH drop
6) Measure and address any phosphate issues
7) If your light's tubes have been running longer than 6mo, replace them
(oh, I don't know what lights you have - will depend on that)

Well, that's my $0.02, anyway. Good luck!! 
Regards,

Will


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## naturelady (Dec 14, 2009)

Wow, tons of good information in there, thanks! 

To address a couple things...

I do not currently have a phosphate test kit, but have a friend who might- will check to see. Or go buying...

The nitrates might not be at 0 anymore. That reading was taken a couple days ago, after the guppies were added and before the cory cats were added. I need to measure again.

As far as pH/KH/GH... those readings are with my tap water already diluted 50% with RO water. So I can take it down more by adding more RO. The question is, how quickly can I change things with RO? I'm guessing to do a 50% WC and refill with all RO water would be a drastic change for the fish.

I keep my tank full to minimize surface agitation, but obviously can't completely eliminate it.

Oh, and the HC is definitely growing, although slowly. So I think it will eventually get where I want it, just going to take a (long) while.


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## naturelady (Dec 14, 2009)

So, did I mention that I just inherited this tank and setup from a friend? I mean, I always thought the gallons added up really quick when I did water changes, but okay. Who minds that?

I got into a discussion with hydrophyte today about tank dimensions, and things just weren't adding up. So I pulled out a ruler and actually measured my tank. Its 15 gallons. :icon_redf :icon_redf :icon_redf


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## willbldrco (Mar 24, 2007)

naturelady said:


> Wow, tons of good information in there, thanks!


You're welcome! 



> I do not currently have a phosphate test kit, but have a friend who might- will check to see. Or go buying...


Yeah, that would be good to know. If your phosphates are high and your nitrates are very low, your plants are basically stalled waiting for nitrates. Meanwhile phosphates keep accumulating (not good). Once you get those back up to good levels, your plants will start consuming phosphate (and other nutrients used in photosynthesis).



> As far as pH/KH/GH... those readings are with my tap water already diluted 50% with RO water. So I can take it down more by adding more RO. The question is, how quickly can I change things with RO? I'm guessing to do a 50% WC and refill with all RO water would be a drastic change for the fish.


The fish you have won't be affected much by changes in KH or pH. In fact most fish are resilient to such changes. Your shrimp might be, however. I would do a 20% water change with nothing but distilled water and remeasure pH and KH. Keep doing that every other day or so until your pH and KH are at 7.0 and 5-6 dK, respectively. Or whatever your targets are (most shrimp prefer soft water with lower pH anyway). After you get it down a level more suitable for dissolved CO2, try to keep it at those levels and monitor your algae situation.



> I keep my tank full to minimize surface agitation, but obviously can't completely eliminate it.


One trick here is to point your return valve (if you have one) downward so the return current spreads out over the bottom of the tank. This minimizes surface current (where the gas exchange happens).



> So I pulled out a ruler and actually measured my tank. Its 15 gallons.


LOL!! You know what might surprise you more: Actually measure the water you put into the tank after all the substrate, rocks, plants, equipment, etc. are there. I recently did that for a 90gal tank and was shocked to find that I only added 70gal of water!!! As I added each 5gal, I put a mark on the side of the tank with a sharpie. This altered my IE numbers since when I did a "50%" water change, I was really only pulling out 35gal, not 45gal as one would expect for a 90gal. You might want to make the same markings in 1gal increments to see exactly how much you are replacing during water changes.

Good luck!

Will


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## DarkCobra (Jun 22, 2004)

Willbldrco,

1) What pH would you suggest as a good compromise between H2CO3 availability and fish safety?
2) If I don't have access to RO water, and I can't further raise my CO2 due to fish gasping, are there any downsides to using a pH reducer (such as HCl) to lower the pH?


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## willbldrco (Mar 24, 2007)

DarkCobra said:


> Willbldrco,
> 
> 1) What pH would you suggest as a good compromise between H2CO3 availability and fish safety?


The lowest I've gone is 6.2 and during that time I didn't see any adverse effects on the fish. I have SSEs, ottos, various tetras. I don't have shrimp so I can't speak for those.



> 2) If I don't have access to RO water, and I can't further raise my CO2 due to fish gasping, are there any downsides to using a pH reducer (such as HCl) to lower the pH?


Oh wow! If your fish are gasping via CO2 injection, you should have a pretty low pH. What is your KH?

I've used pH altering chemicals in the past and have found that unless you constantly monitor and adjust, you're going to get swings in pH. That's probably not that bad for the fish, but it's not health for plants and algae control.

Frankly, the best way to monitor CO2 levels (and greatly minimize the effect buffering has on your readings) is a *drop checker*. I keep mine at green/yellow with happy plants, but no gasping fish. 

Here's an overview of drop checkers:

http://www.njagc.net/articles/co2dropchecker.htm

Regards,

Will


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## DarkCobra (Jun 22, 2004)

willbldrco said:


> Oh wow! If your fish are gasping via CO2 injection, you should have a pretty low pH. What is your KH?


KH is 8°. Some fish stay at the surface when I crank up the CO2 past my current level. I'm fairly new to pressurized CO2 so perhaps I'm being overly cautious, but I'm interpreting that as a sign to back off.

Current pH is 6.6-6.8. That's 38-60ppm CO2 according to a pH/KH calculator. I'm currently using no pH adjusters or buffers other than CO2.

The reason I'm interested in this is because I cannot get my plants to pearl.

I know pearling isn't necessary, but my current inability to get them to pearl at all disturbs me. I've tried higher light, nutrients, CO2, reduced surface agitation - still no trace of pearling.

While reading your post, I remembered that I did get pearling for a while when I first installed pressurized CO2. Prior to that I was using HCl to lower pH, and it had not yet been removed by water changes during the time I observed pearling. Perhaps greater H2CO3 availability was the reason.



willbldrco said:


> Frankly, the best way to monitor CO2 levels (and greatly minimize the effect buffering has on your readings) is a *drop checker*. I keep mine at green/yellow with happy plants, but no gasping fish.


I got one recently. After placement in my tank, it went green and does not shift at all; either when I crank up the CO2 and the fish start hanging around the surface, or when I had a CO2 failure two nights ago and I had no CO2 for at least 12 hours during the night cycle when I run an airstone. I haven't yet figured out what's wrong with it, so I'm disregarding the drop checker's reading for now.


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## willbldrco (Mar 24, 2007)

DarkCobra said:


> KH is 8°. Some fish stay at the surface when I crank up the CO2 past my current level. I'm fairly new to pressurized CO2 so perhaps I'm being overly cautious, but I'm interpreting that as a sign to back off.
> 
> Current pH is 6.6-6.8. That's 38-60ppm CO2 according to a pH/KH calculator. I'm currently using no pH adjusters or buffers other than CO2.
> 
> The reason I'm interested in this is because I cannot get my plants to pearl.


I used to have KH at 9-10 degrees and my drop checker was solid green - like it was St. Patricks day all year long.  Well, it was green during the day and reverted to blue at night when the CO2/lights were out.

When I started cutting my tap with distilled water, it dropped to KH 7 and my drop checker turned to a pale green color during the day and blue at night. When I replaced by old enameled generic gravel with Eco Complete black, it dropped over a few weeks to KH 3-4. My drop checker now stays greenish-yellow all the time (both day and night now). So there is very little buffering at this point. In fact I started adding more tap water with the hope of KH being a solid 4 degrees (I'm preping for discus).



> I know pearling isn't necessary, but my current inability to get them to pearl at all disturbs me. I've tried higher light, nutrients, CO2, reduced surface agitation - still no trace of pearling.


Hmmm... How are your ferts? When my NO3 is at 0, my pearling stops. If my ferts are correct, my lights are not old (I replace every 6 mo), my CO3 is on (runs so fast the bubble checker is a stream of bubbles for my 90gal), I have tons of pearling from all my stems. I've never see any pearling from my slower-growing plants like Java Fern or Anubis, however. Oh, except for when my Anubis flowers, for some reason a stream of bubbles likes to come from the flower stem...

What plants do you have?



> While reading your post, I remembered that I did get pearling for a while when I first installed pressurized CO2. Prior to that I was using HCl to lower pH, and it had not yet been removed by water changes during the time I observed pearling. Perhaps greater H2CO3 availability was the reason.


Assuming there is NO3 available in the water column, I suspect the non-pearling is due to either buffering due to your high-ish KH or old lights. Well, those have been problems for me in the past, at least. 



> I got one recently. After placement in my tank, it went green and does not shift at all; either when I crank up the CO2 and the fish start hanging around the surface, or when I had a CO2 failure two nights ago and I had no CO2 for at least 12 hours during the night cycle when I run an airstone. I haven't yet figured out what's wrong with it, so I'm disregarding the drop checker's reading for now.


Yes, this was my experience with the drop checker as well (see above). What is your CO2 injection rate (bubbles/sec or bubbles/min)? Do you have alot of plants? Curious...

Will


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## DarkCobra (Jun 22, 2004)

willbldrco said:


> I used to have KH at 9-10 degrees and my drop checker was solid green - like it was St. Patricks day all year long.  Well, it was green during the day and reverted to blue at night when the CO2/lights were out.


St. Patty's green is exactly what I see too. 

Hmm.. Maybe I'm misunderstanding, but I thought the point of the drop checker is to make tank KH/buffers irrelevant to CO2 measurement, because only the reference solution's KH matters?

For the reference solution, I started with tap water. Let it age for 24 hours, verified KH is 8°, then diluted 50% with distilled water. KH was then verified as 4°. It may not be perfectly accurate, but I wouldn't expect it to fail this badly.



willbldrco said:


> Hmmm... How are your ferts? When my NO3 is at 0, my pearling stops. If my ferts are correct, my lights are not old (I replace every 6 mo), my CO3 is on (runs so fast the bubble checker is a stream of bubbles for my 90gal), I have tons of pearling from all my stems. I've never see any pearling from my slower-growing plants like Java Fern or Anubis, however. Oh, except for when my Anubis flowers, for some reason a stream of bubbles likes to come from the flower stem...


Ferts should be at least adequate. Some N and plenty of P from fish/tapwater alone. Daily dosing based on EI, but I've reduced the N/P and increased the K/iron/micros. Weekly water change is 33% instead of 50% due to some sensitive danios. Will be increasing the N/P soon.

Lighting is medium. 2x 17W 24" T8, each in a separate fixture; plus 2x 23W daylight spiral fluorescents in a 10g incandescent fixture. All are over a clean glass cover, and are under 6 months old. I arrange these to put the brighter light where I need it most. I'm aware this is insufficient for substantial pearling.



willbldrco said:


> What plants do you have?


Wisteria
Bacopa
Cabomba
Sword
Golden Lloydiella/Golden Creeping Jenny
Glossostigma Elatinoides
Nesaea Sp. 'Red Leaved'
Hemianthus Micranthemoides 'Baby Tears'

All are healthy, though some aren't ideally suited to my lighting, and grow slowly. On the other hand, the wisteria wants to take over the tank.



willbldrco said:


> Assuming there is NO3 available in the water column, I suspect the non-pearling is due to either buffering due to your high-ish KH or old lights. Well, those have been problems for me in the past, at least.


After my last post, I slowly brought my pH down to 6.2 with a bit of HCl. Just before lights-out, I saw slight pearling from the fast growers! :bounce: I can't wait to see what effect this has over the next few days.



willbldrco said:


> Yes, this was my experience with the drop checker as well (see above). What is your CO2 injection rate (bubbles/sec or bubbles/min)? Do you have alot of plants? Curious...


No bubble counter. Bare CO2 line goes directly into opaque canister filter intake. If I shut off the filter, I can hear the bubbles. Too fast to count exactly, estimate is 15bps. With this setup, adjustments for a wide range around current level change only the bubble size (the sound changes but not the count); so bubble rate is probably useless here for comparison purposes.

Tank is a bit light on plants at the moment; it recently got a massive cleaning, trim, and rescape to make room for some new plants to grow, like the glosso.

Also, I'm using plain gravel. The tank belongs to me and my girlfriend, and we have an agreement. She handles the scaping, most plant and fish selection, and other aestetic choices. I do everything else to make her choices actually work.  It took a while to convince her on the nutrients, lighting upgrades, and CO2; she feared they would harm the fish. That's one reason I'm so cautious when fish show any possible sign of CO2 stress, accidental kills would be a big setback. But despite periodic attempts to change her mind, she still insists on the gravel due to appearance alone. If I ever succeed, it will be swapped for the 50lb. bag of black Soilmaster Select I have in an instant! At least the gravel has no effect on hardness I can detect.

So my tank isn't exactly "by the book". 

Thanks for the excellent post on carbon availability. I've seen the info before, but I'd never considered adjusting anything but the CO2. The reappearance of pearling is promising, and it's comforting to have a visual indicator that everything is alright.


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## willbldrco (Mar 24, 2007)

DarkCobra said:


> St. Patty's green is exactly what I see too.
> 
> Hmm.. Maybe I'm misunderstanding, but I thought the point of the drop checker is to make tank KH/buffers irrelevant to CO2 measurement, because only the reference solution's KH matters?


Yes, you're right, the drop checker does the best job of measuring the concentration of dissolved CO2 - regardless of buffering (KH) capacity of your water. However, it says nothing about the _ease of changing_ that concentration (and by association, the pH) to what you want it to be. I was trying to explain that if you wanted to make it easier to change the color expressed by your drop checker by simply changing your CO2 rate, you could reduce your KH (buffering ability). Once I got my KH down to 7 and lower, I found I could easily go from always-green to green-yellow by simply bumping up my CO2 stream (no pH down chems needed).

The less carbonates in the water (lower KH), the more effect the CO2 you inject will have on lowering your pH (and thus be more concentrated in a form available to your plants).



> For the reference solution, I started with tap water. Let it age for 24 hours, verified KH is 8°, then diluted 50% with distilled water. KH was then verified as 4°. It may not be perfectly accurate, but I wouldn't expect it to fail this badly.


I wonder how it would compare to the drop checker in my tank. Can you bring yours over? 

Seriously, your method makes sense (assuming you can trust your KH test kit).



> Ferts should be at least adequate. Some N and plenty of P from fish/tapwater alone. Daily dosing based on EI, but I've reduced the N/P and increased the K/iron/micros. Weekly water change is 33% instead of 50% due to some sensitive danios. Will be increasing the N/P soon.


When I first broke down and bought N/P test kits, I was shocked to find I had huge amounts of phosphate and zero nitrates! I had to dump in 3g of dry KNO3 before my water registered at the 5ppm section of the color chart! So I use test kits from time to time when my tank starts to show signs of issues and I'm at a loss as to why.

Still, I can see that if your plants are happy and your algae is under control, why bother testing? IE works very well once you get into a routine. I dose on my weekly water change days and sometimes a few days later. When everything is on the rails with my tank, I can go months without testing. It's when I make big changes or see issues that I fall back on testing (big plant swap out, fish load change, substrate change, algae blooms, etc).



> Lighting is medium. 2x 17W 24" T8, each in a separate fixture; plus 2x 23W daylight spiral fluorescents in a 10g incandescent fixture. All are over a clean glass cover, and are under 6 months old. I arrange these to put the brighter light where I need it most. I'm aware this is insufficient for substantial pearling.


Yeah, if it's substantial pearling you want, you'll want to shoot for more light. One of the gurus on plantedtank (I forget who) once told me this when I expressed an interest to upgrade to 3watts/g: Something like, "Your plants will love the extra light, but get ready for everything to happen much faster: pruning needs, algae blooms, nutrient use, etc." Boy was he right. 



> Wisteria
> Bacopa
> Cabomba
> Sword
> ...


Well, that should keep your N/P in check! 



> After my last post, I slowly brought my pH down to 6.2 with a bit of HCl. Just before lights-out, I saw slight pearling from the fast growers! :bounce: I can't wait to see what effect this has over the next few days.


Awesome! You'll have to post your pearling observations. It would be interesting to see what effect that pH drop has on your drop checker color.



> No bubble counter. Bare CO2 line goes directly into opaque canister filter intake. If I shut off the filter, I can hear the bubbles. Too fast to count exactly, estimate is 15bps. With this setup, adjustments for a wide range around current level change only the bubble size (the sound changes but not the count); so bubble rate is probably useless here for comparison purposes.


Whatever works!  These fancy tools like bubble counters just make it easier to express whats going on via forum threads.



> Also, I'm using plain gravel. The tank belongs to me and my girlfriend, and we have an agreement. She handles the scaping, most plant and fish selection, and other aestetic choices. I do everything else to make her choices actually work.  It took a while to convince her on the nutrients, lighting upgrades, and CO2; she feared they would harm the fish. That's one reason I'm so cautious when fish show any possible sign of CO2 stress, accidental kills would be a big setback. But despite periodic attempts to change her mind, she still insists on the gravel due to appearance alone. If I ever succeed, it will be swapped for the 50lb. bag of black Soilmaster Select I have in an instant! At least the gravel has no effect on hardness I can detect.


LOL! I love it! Sounds like a great couples project. I had a nice tank going for 2-3 years using recycled 10 year old dime-store-quality aquarium gravel, and it worked just fine. Here's a pic of that tank:










Once I swapped it out with Eco Complete, I noticed two things immediately:


It was much easier to keep my KH where I wanted it (lower)
Certain plants really took off (Vals, anything reddish)

So I guessed that 1) something was leaching from the gravel to raise my water hardness (feeding my KH levels), and 2) Eco Complete was supplying iron in a form not available to my plants before. Seriously - my Vals went from so-so to 3" long monsters with TONS of side shoots. But these are just guesses based upon what I observed.



> So my tank isn't exactly "by the book".


Those are the most interesting. 



> Thanks for the excellent post on carbon availability. I've seen the info before, but I'd never considered adjusting anything but the CO2. The reappearance of pearling is promising, and it's comforting to have a visual indicator that everything is alright.


You're welcome! Good luck with your tank and eventually getting your dream substrate. 

Will


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## DarkCobra (Jun 22, 2004)

willbldrco said:


> Once I got my KH down to 7 and lower, I found I could easily go from always-green to green-yellow by simply bumping up my CO2 stream (no pH down chems needed).


That suggests to me that the drop checker is sensitive primarily to CO2 in the form of carbonic acid, and not so much in the form of carbonate or bicarbonate. Is that correct?



willbldrco said:


> Yeah, if it's substantial pearling you want, you'll want to shoot for more light. One of the gurus on plantedtank (I forget who) once told me this when I expressed an interest to upgrade to 3watts/g: Something like, "Your plants will love the extra light, but get ready for everything to happen much faster: pruning needs, algae blooms, nutrient use, etc." Boy was he right.


Indeed he was! I'm still learning at this light level and enjoying it, but also itching to go further. The next big upgrade will be 3x F39T5HOs with Icecap reflectors on a dimming ballast, so I can go any speed I want. 



willbldrco said:


> Awesome! You'll have to post your pearling observations. It would be interesting to see what effect that pH drop has on your drop checker color.


Pearling was better today, since this was the first full day since the pH adjustment. But still no change on the drop checker.

That is (was) a lovely tank BTW.


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## willbldrco (Mar 24, 2007)

DarkCobra said:


> That suggests to me that the drop checker is sensitive primarily to CO2 in the form of carbonic acid, and not so much in the form of carbonate or bicarbonate. Is that correct?


The indicator solution contained in the drop checker will be affected by protons (H+) in the aquarium water. The concentration of free protons is measured by pH. Lots of H+ = low pH. Small number of H+ = high pH.

CO2 injected into water will create carbonic acid (H2CO3) which exists as free protons and bicarbonate (which acts as a base) in water:

H2CO3 ⇌ HCO3− + H+

But notice that if you dump a bunch of bicarbonate in the water (like sodium bicarbonate), there will be lots available to combine with the free protons (and other positivly charged ions) which lessens the concentration of protons (pushes the equation to the left). So bicarbonate in the water "sucks up" the acidifying power of CO2 (or any other acid, like your HCL) and thus will affect the pH (drop checker color).

So to answer your question, carbonic acid (CO2) affects the drop checker color, but bicarbonate affects how easily it will change. If your KH is high (lots of carbonates in the system), the protons added by CO2 injection will be sucked up (buffered) so that the acidifying effects are minimized.

Thus, low KH (few carbonates) affect the speed/ease of altering your pH via CO2 injection.

At the risk of beating a dead horse, low KH means I only need to add a little CO2 to change the pH significantly. High KH means I have to add lots of CO2 (or lots of other acid as you may find with your use of HCL) before the pH will change.



> Pearling was better today, since this was the first full day since the pH adjustment. But still no change on the drop checker.


With your KH value this doesn't surprise me. Your tank has a high buffering capability and will likely suck up lots of acid before you see that drop checker color change.



> That is (was) a lovely tank BTW.


Thanks! I sorta miss it. 

Will


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## DarkCobra (Jun 22, 2004)

I wish my last chemistry class wasn't 20 years ago, I had to read that a few times. 

But I think I finally understand.

As you said, CO2 combines with H2O to form H2CO3, which exists in solution as HCO3- and H+ ions. I recall this transformation is easily reversible and that CO2 can be reformed; and that at a water/air interface, this transformation proceeds constantly in both directions, tending towards equilibrium.

The reformed CO2 is what actually enters the drop checker. But if an alkaline buffer is tying up H+ ions, then those ions aren't available for the reformation process; so CO2 reformation slows.

Seems like the common statement that "a drop checker measures dissolved CO2", which I always took literally, is a partially inaccurate oversimplication.

If I'm correct so far (please tell me if I'm not), something else just occured to me as I'm typing.

By adding additional H+ ions from HCl, I've made it easier for CO2 to reform at the drop checker's water/air interface, which should make it change color. But I'm also making it easier for CO2 to reform at the much larger water/air interface at the top of the tank! That would increase my tank's rate of CO2 loss, perhaps just enough that it explains why I saw no change in the drop checker's color.

If that's true, I should see a upwards rebound from the 6.2 pH I measured immediately after adding HCl. And if I do, I may need to turn the CO2 up to compensate.

I'm off to play with the tank now. 

EDIT: Tank has indeed rebounded to 6.6 pH. There could be other reasons for that, so I'm going to slowly increase the CO2 and get a second opinion from the plants and fish.


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## willbldrco (Mar 24, 2007)

DarkCobra said:


> I wish my last chemistry class wasn't 20 years ago, I had to read that a few times.
> 
> But I think I finally understand.
> 
> ...


Wow! That's a really good analysis!

The only thing I can think to add to your most excellent summery is this: When you add HCL, yes, you're adding protons (H+), but you're also adding an equal amount of negatively charged chloride ions (CL-) which acts as a week base. Similarly bicarbonate does not exist by itself as a negatively charged ion either (HCO3-), but is likely accompanied by some other positively charged ion like sodium (Na+, i.e, sodium bicarbonate) or, if further ionized to carbonate, calcium ions (Ca++, i.e, calcium carbonate). So things can get quite "soupy" at high KH.

At high KH, I find the chemistry is a big mess. I can relate to your rusty 20yo chem knowledge (*pulling hair out*). 

For me, things get simpler when buffering is minimized (less animals are in the water). Working at a low KH allows me to more easily manage pH (and by association, dissolved CO2) because I'm (mostly) working with just CO2 and water. Once my KH is below 6-7, I can do thing like:


Oh, is that BBA on that leaf??!! Ok, up my CO2 injection by 10-20%
I want more pearling. Ok, I'll add 10 more bubbles per minute of CO2 and test my macro ferts to make sure they are available during photosynthesis. (as long as I have enough light)
Oh man - my drop checker is canary yellow and my fish are hanging around the surface. Ok, I'll crank my CO2 back by 10 bubbles/minute

When my KH was higher, I had to work more to make changes in the carbon cycle (add stuff like Excell and pH down chems). Now with KH at 4 degrees, I just turn the knob on my needle regulator to tweak my carbon/pH. 

Will


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## plantedtankdreamer (Apr 18, 2015)

*New to Planted Tanks: How to keep them clear of algea*

Hello, I am new to planted tanks and tired to set up a 26 gallon planted tank. Algae of all sorts is now growing and I am wondering how to bring it into balance. I would love to see the shine of algae free plants again.  String algae, strange tufted fuzzy black algae, and green algae

Set Up:
48W T5HO dual for the lighting
Excel Flourish for CO2
No Fertilizer
Carib Sea substrate
UV filter
Hanging filter
Varying hours of light (trying to cut back to counter algae) 

Fish: 
6 Pepper Cories 
4 Ottos
2 German Blue Rams
6 Glowlight Danios
2 Mollies (brought in from another tank to help eat string algae) 

Plants: 
Anubias, Amazon Sword, Java Fern and Wendii 

Any suggestions on how to get this tanks back into balance would be great! Thanks!


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