# CO2 - How much is needed?



## mistergreen (Dec 9, 2006)

Yup, I was binging on Tropica videos the other day and all their tanks are around 25mg/L (ppm) CO2.

You can probably bump up the PAR to get better growth. This is not a new idea but what about a constant low CO2 24/7 which DIY yeast provides? Those with CO2 tanks could probably do 15-25ppm safely for 24/7.


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## Seattle_Aquarist (Jun 15, 2008)

Hoppy said:


> My drop checker, using 1 dKH water in it, indicates that I most likely have about 3-10 ppm of CO2.


Hi Hoppy,

I know that a 4.0 dKH indicator solution is standard for drop checkers so we can use the standard PH scale to determine PPM (PH 6.6 color = 30ppm). How do you do the math with 1.0 dKH water indicator solution or are you using something like this chart?


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## DennisSingh (Nov 8, 2004)

> I have about 30-35 PAR light intensity, good low light, and had very unimpressive growth of my plants, using only Excel (Metricide) as a carbon source. I added a DIY CO2 system along with the Excel, and now the plant growth is much improved, although still slow. My drop checker, using 1 dKH water in it, indicates that I most likely have about 3-10 ppm of CO2.


I got to say that despite varying opinions against, excel is not a source of C. its a sterilizer. I have this engrained in my head. When overdosed it'll cause some Shiz to happen, and overdosed can also very well melt or kill a plant. Someone then explain to me this: with excel how many ppm's C are you adding? With co2, how come you can overdose and not have the same ill effects? stunting i'd say vs obliterating the plant. 

For the rest light and co2 and o2 seem to correlate better than any dosing schedule regime in having a successful tank.


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## Seattle_Aquarist (Jun 15, 2008)

StrungOut said:


> I got to say that despite varying opinions against, excel is not a source of C. its a sterilizer. I have this engrained in my head. When overdosed it'll cause some Shiz to happen, and overdosed can also very well melt or kill a plant. Someone then explain to me this: with excel how many ppm's C are you adding? With co2, how come you can overdose and not have the same ill effects? stunting i'd say vs obliterating the plant.
> 
> For the rest light and co2 and o2 seem to correlate better than any dosing schedule regime in having a successful tank.


Hi StrungOut,

Good questions! Yes glutaraldehyde, the main ingredient in Seachem Excel is a sterilizer. And you are correct, it can cause issues when overdosed in a tank with plants, fish, shrimps, etc. Seachem Excel / glutaraldehyde does not add any ppms of CO2 to an aquarium but it does make carbon molecules available to plants for use in photosynthesis. 

There are several chemical formulas for glutaraldehyde such as CH2(CH2CHO)2. All of the formulas show the existence of carbon molecules (the "C"'s in the formula) in the solution. Tom Barr explained it to us in his talk at GSAS in 2010. Basically Dr. Barr (yes he has his doctorate) explained the similarity of the glutaraldehyde molecule to molecules manufactured during the Calvin Cycle of photosynthesis allows the glutaraldehyde to provide its carbon molecules and enhance the productivition of sucrose, the building block that plants use for growth. 

For the biochemists out there Seachem did a paper on the subject many years ago. In it they state:


> The chemical structure of Flourish Excel™ is quite similar to some of the products of photosynthesis such as Ribulose 1,5-bisphosphate and 2’-carboxy-3-keto-D=arabinitol 1,5 bisphosphate. Flourish Excel™ possesses the same basic 5-carbon chain seen in these molecules.


 which is what Tom Barr explained to us non-biology majors in terms we could understand.

I'm sure I did not explain it as well as Tom Barr could, maybe he will weigh in if he gets a chance.


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## houseofcards (Mar 21, 2009)

StrungOut said:


> I got to say that despite varying opinions against, excel is not a source of C. its a sterilizer.


I've always kinda felt the same way. Even though it's marketed as a nutrient and has the secondary effective of being an algaecide, I feel it's the other way around. Has anybody actually setup two identical tanks and seen the difference with and without Excel.


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## DennisSingh (Nov 8, 2004)

Seattle_Aquarist said:


> Hi StrungOut,
> 
> Good questions! Yes glutaraldehyde, the main ingredient in Seachem Excel is a sterilizer. And you are correct, it can cause issues when overdosed in a tank with plants, fish, shrimps, etc. Seachem Excel / glutaraldehyde does not add any ppms of CO2 to an aquarium but it does make carbon molecules available to plants for use in photosynthesis.
> 
> ...


You got a link? I'd like to actually hear it from him myself lol my bad Roy
@plantbrain



> I've always kinda felt the same way. Even though it's marketed as a nutrient and has the secondary effective of being an algaecide, I feel it's the other way around. Has anybody actually setup two identical tanks and seen the difference with and without Excel.


Yes even though what Roy stated, I don't see it

I don't see plants taking it in and respirating o2 that way.

All I can say and seen it done is that it tackles destroys algae.


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## dukydaf (Dec 27, 2004)

Hoppy said:


> Generally we tell people starting with CO2 that they should get 30 ppm of CO2 into the water - that's what the plants need. *This is not good advice!*
> 
> Tropica has a pretty good, brief article on this subject: Fertiliser and CO2 for your aquarium. - Tropica Aquarium Plants This article says "A bit of CO2 (e.g. 3-5 mg per L) is better than nothing. Plants that are marked "Medium" require about 10-15 mg CO2 per L, but "Advanced" plants require 15-30 mg CO2 per L."


I am not trying to be contrarian, nor defend/attack anything or anybody. I just want to provide a different perspective. All the respect Hoppy for your experience, knowledge and interesting comments and topics. 

I feel we could argue the same for every nutrient recommended level. Few aquariums *need* 3ppm PO4 weekly. Furthermore, what one aquarium *needs* today might not be the same as tomorrow or after a big trim. I will still recommend this level, provide it all the time as there is nothing wrong with a little extra with the 50% wc. Always changing it increases the likelihood of running into deficiencies. 

Then, the word * need* is not very precise. My aquarium can survive with 2ppm PO4, but it does a lot better with 4ppm PO4. Which level is needed ?

I use PO4 for my arguments as CO2 is even more problematic. I think most of us had aquariums where the KH/pH chart gave us large overestimation of our CO2 levels, other where the indicator turned yellow but algae/plant problems were solved with extra CO2. If your measuring tool says you have 30ppm, add a very large confidence interval around it.

CO2 is also very variable at one time-point in different places of aquarium. Water that has 60ppm at the exit from the reactor could end up with 15ppm at filter intake after passing through plants and surface layer. How, when, where is the measurement to be done to get an accurate estimation of 30ppm is often a problem for newcomers.

As you rightly point out, light is the main driver of CO2 demand. However things are not as easy as only looking at light levels at the ground. Plants' *needs * also vary across the height of the tank... shaded bottom layer is ok with less, the nearer the light the more CO2 needed. Same light and aquarium, one aquascape can have lower CO2 as it is mostly grass; the other needs more because R. macrandra will get damaged near the light. Which of these CO2 need levels should be targeted as a general advice ?

Is there any limitation in the tank ? Less CO2 is ok then. Tom Barr even argues that low PO4 could help reduce plant problems in tanks that would be CO2 limited. 

Like all the nutrients, C needs to be provided in non-limiting amounts for good plant growth. If you are unable to provide this level (no matter the reason) the best way forward is to reduce the light intensity. A large number of plants can survive and grow at lower light intensities. What exact ppm is non-limiting depends on your specific aquarium and point in time. For this reason I consider it good advice to recommend 30ppm for non-limiting CO2 levels in medium-high light setups. 

Further reading: The light limiting growth management method - Aquarium Plants - Barr Report


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## GrampsGrunge (Jun 18, 2012)

Having just started a DIY CO2 system in my dirted 20 gallon tank, it's undersized for a reason. The soil is supposedly a source for CO2.

But since I also grow plants that a water column feeders, I think a supplemental source of CO2 seems to be working well. One thing about DIY CO2 with yeast and sugar is that the output is temperature and age dependent. As the yeast culture warms the output increases and as it ages the output slows. I used to put my DIY CO2 bottles over my light ballasts so they would warm up as the ballasts warmed, which bumped the CO2 output a small amount to catch up with the light.


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## Seattle_Aquarist (Jun 15, 2008)

Hi All,

It's funny that @dukydaf should mention Tom Barr's '_Light Limiting Growth Method_', that was the exact presentation Tom Barr was making to GSAS when he discussed the Calvin Cycle and how glutaraldehyde can provide additional carbon atoms/molecules. On a side note, he also explained that the 'pearling' we see on our plants was not the result of plants 'breaking down' CO2 into oxygen but rather it was the plants 'breaking down' water to generate the O2 bubbles....it was an excellent talk and I revisit it regularly as part of the GSAS video library.


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## Hoppy (Dec 24, 2005)

Seattle_Aquarist said:


> Hi Hoppy,
> 
> I know that a 4.0 dKH indicator solution is standard for drop checkers so we can use the standard PH scale to determine PPM (PH 6.6 color = 30ppm). How do you do the math with 1.0 dKH water indicator solution or are you using something like this chart?


You don't have to do the math - the chart works fine. Note that at 1 dKH, you start getting green at about 3 ppm of CO2 and you start getting near yellow at about 12 ppm. With a tank full of green plants (and, sometimes, algae) it is hard to determine exactly how green the drop checker water is (although the best drop checkers make it a lot easier), so there is a fairly wide range of possible CO2 ppms for "green". But, it is sufficiently accurate to determine that you are, in fact, raising the CO2 level in the water with the DIY CO2 you are using.



StrungOut said:


> Someone then explain to me this: with excel how many ppm's C are you adding? With co2, how come you can overdose and not have the same ill effects? stunting i'd say vs obliterating the plant.


It doesn't matter how many ppm of C you are adding. Any planted aquarium will have lots of C in it - the plants are a big "source" of C, for example, as are the fish. What the plants need is bioavailable C, which can be in the form of CO2, which the plants evolved to use, or a chemical like glutaraldehyde, which fortuitously the plants can get C from.


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## Hoppy (Dec 24, 2005)

houseofcards said:


> Has anybody actually setup two identical tanks and seen the difference with and without Excel.


Yes, although I can't link to any writeups about it. Many of us have done the equivalent experiment by adding Excel to a low light tank that had plants barely growing, and saw a significant increase in the growth rate. I have also then doubled the Excel dosage from 1 ml per 10 gallons of water to 2 ml per 10 gallons, and saw another significant increase in the growth rate. When I used a higher dosage I didn't see nearly as much improvement, but did see a lot more damage to vals. I don't think there is any reason to doubt that Excel works.


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## DennisSingh (Nov 8, 2004)

Hoppy said:


> Yes, although I can't link to any writeups about it. Many of us have done the equivalent experiment by adding Excel to a low light tank that had plants barely growing, and saw a significant increase in the growth rate. I have also then doubled the Excel dosage from 1 ml per 10 gallons of water to 2 ml per 10 gallons, and saw another significant increase in the growth rate. When I used a higher dosage I didn't see nearly as much improvement, but did see a lot more damage to vals. I don't think there is any reason to doubt that Excel works.


Low tech, low schmeck. Do it in a high light tank, the excel will get the plants no where, where pressurized co2 or diy whichever will. 

Correct me if i am wrong.

In a low tech tank there are more variables and room for screw ups. The "excel" eliminated whatever algae is left hence better plant grow.

Do it with high light, excel only see how much you can put in and so on and see where your plants are at.

Thesess are bold statements


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## Clinton Parsons (Apr 11, 2016)

When people refer to nutrient level ranges, what matters: the actual range or the presence of the nutrients?

For example, blood glucose needs to be in a range around 80-110 or so. It needs to stay in this range. If you had a bloog glucose level of 30, you'd go into hypoglycemic shock and the fact that you still have the presence of glucose doesn't matter: you're toast. 

Can a plant absorb nitrate better at a range of 10-15 vs. 1-5? Or is it going to suck up nitrate at the same rate as long as it is present? W ill a plant absorb more phosphate (or absorb it more easily) at 1-2 ppm vs. 0.05-.1 ppm, or is it irrelevant as long as phosphate does not reach zero? 

I hope I explained what I meant with that example. I have always wondered this. We never covered anything like this in Botany or Plant Ecology.


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## Delapool (Mar 12, 2016)

StrungOut said:


> Low tech, low schmeck. Do it in a high light tank, the excel will get the plants no where, where pressurized co2 or diy whichever will.
> 
> Correct me if i am wrong.
> 
> ...




Worse week and a bit of my life when I tried it in my tank when the co2 bottle ran out. Under high light I just got bad growth even dosing 6 x normal.


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## houseofcards (Mar 21, 2009)

Hoppy said:


> Yes, although I can't link to any writeups about it. Many of us have done the equivalent experiment by adding Excel to a low light tank that had plants barely growing, and saw a significant increase in the growth rate. I have also then doubled the Excel dosage from 1 ml per 10 gallons of water to 2 ml per 10 gallons, and saw another significant increase in the growth rate. When I used a higher dosage I didn't see nearly as much improvement, but did see a lot more damage to vals. I don't think there is any reason to doubt that Excel works.


I figured someone would have done this since it's pretty simple to test. Makes me feel better that you did test it and you observed visible growth benefits. I think I might do this myself and see what effect it has on a few different plant types.


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## mistergreen (Dec 9, 2006)

If you can find potassium gluconate or mono potassium glutamate, it'll be a nice substitute to excel or glutaraldehyde. The formers are human consumable, the latter, poisonous. Buy it pure is tricky though. 

I guess monosodium glutamate would work to but you get that Na in the mix.


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## Hoppy (Dec 24, 2005)

The only point of this thread was to say that it isn't necessary to give up the idea of DIY CO2, for lower light tanks, just because you can't get 30 ppm of CO2 that way. Any amount of added CO2 is an improvement over no added CO2, and for lower light tanks you can see the benefit from even small amounts of added CO2. If you use Metricide instead of Excel, and a modest DIY CO2 set-up you can increase your enjoyment of planted tanks, with only a small expense. (Yes, over the long haul, DIY CO2 costs more than pressurized CO2, but you avoid the big initial cost.)


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## dukydaf (Dec 27, 2004)

Fully agree Hoppy, even low levels bring improvement, and as long as light is low enough you will not have major algae problems.

Actually, I managed to gas some fish as a child when using DIY yeast CO2 so you can easily go over 30-60ppm, at least in the first 3 days. And this very high-very low inconsistent levels created many problems. It was hard to keep consistent levels even by using 3 bottles. 

A good CO2 system can last several decades so if you are into growing plants for good it is a good investment. Other than the bottle, the equipment holds a good resale value.


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## jrill (Nov 20, 2013)

Good thread. Hoppy, I think you have inspired me to fire up my citric acid co2 system on my low light, metricide 20 long.

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## rstampa (Jan 29, 2017)

Sorry, but I must say that you should not run co2 24/7. Plants give of co2 at night and take in o2. So I ingress the co2 by increasing air stone etc higher at night. The fish are giving co2 and o2 all the time. Consider these factors and make adjustments accordingly. 
Hope this helps a little.


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## Malakian (Aug 23, 2014)

mistergreen said:


> Yup, I was binging on Tropica videos the other day and all their tanks are around 25mg/L (ppm) CO2.
> 
> You can probably bump up the PAR to get better growth. This is not a new idea but what about a constant low CO2 24/7 which DIY yeast provides? Those with CO2 tanks could probably do 15-25ppm safely for 24/7.


Just watched most of their "layout" videos too. Man, they use way less Co2 and ferts than me (most?), and 2-3x more light. Interesting to say the least.

I'm at 1.4-1.5 ph drop from Co2 (something like 40-50 ppm/mg pr L I'm guessing. Yellow DC's), 1/2w pr liter 16 inch from water surface, and waaaay more ferts, over 10x as much. Still not as happy plants as them, and algae


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## Dman911 (Nov 24, 2016)

1.5 PH drop would put you approx. 96ppm co2

Dan


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## clownplanted (Mar 3, 2017)

Dman911 said:


> 1.5 PH drop would put you approx. 96ppm co2
> 
> Dan




Yup. I hit 1.2 which puts me at like 45ppm co2

But I run powerheads that give good surface movement 24/7. This in turn allows you to run more co2 with no ill effects to livestock. If I was to try and run 45ppm of co2 with no surface movement guaranteed they would be at the surface gasping for air. Yes I use more co2 but co2 is cheap and all inhabitants including the plants seem happier with the surface movement. Also the plants for me really do pearl harder. 


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## Malakian (Aug 23, 2014)

Dman911 said:


> 1.5 PH drop would put you approx. 96ppm co2
> 
> Dan


That can't be correct. If you look at the charts, yes that is where I should be aprox. But all Fish should of been dead then, or at least the shrimp. Everything seems fine though. And I measured PH drop with both a calibrated pen, and drop tester.
And plants don't really pearl much before I hit 1.3ph drop. Weird. Maybe the chart gets a little wonky at high level, I don't know.

Edit: Did the KH/PH test just now. Used 10ml test water so each drop equals 0.5KH, measured 3KH. PH at 6.04, so aprox 90ppm co2 there too. HOW!?


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## Dman911 (Nov 24, 2016)

It's approx. 2-3ppm is what your water should be at equilibrium. We assume 3ppm as it's the higher end to be safe. Let's say yours is close to 2ppm, each .3 drop in PH will double the co2 concentration. That would put you at approx. 64ppm. This is why co2 can only be approximated with the type of equipment we use to measure and a lot of hobbies gauge by plant and fish reaction as you see at the numbers can vary greatly. There is also the question of how accurate the equipment we are testing with.

Dan


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## Dman911 (Nov 24, 2016)

Just to add plants pearling is only a sign of water being saturated with oxygen. If you increase your surface agitation it will more than likely stop but the plants will still be phtosynthesizing at the same rate and be just as healthy. 

Dan


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## clownplanted (Mar 3, 2017)

Dman911 said:


> Just to add plants pearling is only a sign of water being saturated with oxygen. If you increase your surface agitation it will more than likely stop but the plants will still be phtosynthesizing at the same rate and be just as healthy.
> 
> Dan




My plants actually pearl harder with more surface movement. They are absolutely saturated and the entire tank looks like a soda machine. They have been actually pearling a lot harder since I started good surface movement 24/7 about 3 weeks ago. Before that I would not do any surface movement during photoperiod and they did not pearl as hard. Now I do run about 10ppm more co2 due to more o2 due to more movement but they have never pearled harder since the change. 

In my observation I absolutely feel surface movement is great for the plants and livestock and all signs definitely point to this. 


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## Dman911 (Nov 24, 2016)

clownplanted said:


> My plants actually pearl harder with more surface movement. They are absolutely saturated and the entire tank looks like a soda machine. They have been actually pearling a lot harder since I started good surface movement 24/7 about 3 weeks ago. Before that I would not do any surface movement during photoperiod and they did not pearl as hard. Now I do run about 10ppm more co2 due to more o2 due to more movement but they have never pearled harder since the change.
> 
> In my observation I absolutely feel surface movement is great for the plants and livestock and all signs definitely point to this.
> 
> ...


I agree about the surface agitation being good for both plant and livestock. It could be the increased flow distributing the Co2 better in the tank resulting in more photosynthesis but surface agitation will also aid in the exchange of all gasses back towards equilibrium so the more surface agitation the more it is likely to reduce the effect of pearling. Pearling is nothing more than the water being close to or completely saturated with O2 and therefore the O2 builds up as a bubble and floats to the top as the o2 is released by the plants instead of being dissolved into the water column. This is why you may see a decline of pearling with increased surface agitation even though the plants are still photosynthesizing at the same rate. Its not as much of an indicator of plants health as people think. You can have extremely healthy plants that don't pearl. Plant mass also plays a big role, more plants and faster growing plants will saturate the water faster and tend to pearl more than a tank with minimal slower growing plants.

Dan


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## clownplanted (Mar 3, 2017)

Dman911 said:


> I agree about the surface agitation being good for both plant and livestock. It could be the increased flow distributing the Co2 better in the tank resulting in more photosynthesis but surface agitation will also aid in the exchange of all gasses back towards equilibrium so the more surface agitation the more it is likely to reduce the effect of pearling. Pearling is nothing more than the water being close to or completely saturated with O2 and therefore the O2 builds up as a bubble and floats to the top as the o2 is released by the plants instead of being dissolved into the water column. This is why you may see a decline of pearling with increased surface agitation even though the plants are still photosynthesizing at the same rate. Its not as much of an indicator of plants health as people think. You can have extremely healthy plants that don't pearl. Plant mass also plays a big role, more plants and faster growing plants will saturate the water faster and tend to pearl more than a tank with minimal slower growing plants.
> 
> Dan




Makes sense. Thanks @Dman911 you are da man 

Am sure between the increased flow of co2 and added co2(35ppm upped to 45ppm) is why mine pearled harder 


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## Dempsey (Oct 27, 2009)

@Hoppy Wasn't the 30ppm of co2 range based off of Tom Barr's EI dosing? Correct me if I'm wrong.

I don't think that he states that in the dosing but always recommends that, roughly, for high light tanks. At least that is what has worked for me in the past. I do still struggle with balancing all ferts though(including co2). I think a lot of us do...

Maybe that's where some confusion is coming from?


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## Greggz (May 19, 2008)

Dempsey said:


> @Hoppy Wasn't the 30ppm of co2 range based off of Tom Barr's EI dosing? Correct me if I'm wrong.


Dempsey FYI this was an older thread and unfortunately Hoppy has left the forum. Personally I hope he comes back, as I enjoyed his contributions very much.


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