# Can I add co2 to my walstad tank?



## racialfish (Aug 15, 2006)

So I have a 29 gallon walstad style tank with 1 inch of topsoil and 2 inches of gravel mixxed with flourite. Question is could I add a nutrafin co2 system thing that I have lying around or would this create a giant algae mess. My lighting is 2 shoplight fixtures with 40 watt bulbs=160 watts, obviously it hangs over the sides of the tank so I don't get 5wpg.


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## AaronT (Apr 26, 2004)

It should be fine. I'm adding pressurized CO2 to all 3 of my soil tanks.


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## sb483 (May 29, 2006)

In the long term, however, you might expect to have to empty the tank & start over after one or two years when injecting CO2 - plants release alleochemicals into the soil (from Diana's book), which normally get decomposed by bacteria, but with CO2 injection they accumulate faster than bacteria can break them up. Enough alleochemicals in the soil can prevent further plant growth, which leads to algae taking over the tank.

However if you're keeping the tank for only one or two years anyway, then none of this matters.


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## bpimm (Jun 12, 2006)

You also don't have to put in high levels of CO2. I run my soil tanks with CO2 at about 5-15 PPM, measured with a drop checker, and have good growth.


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## Jane in Upton (Aug 10, 2005)

I have a question for those of you adding some CO2. I don't mean to hijack your thread racialfish, but it's part of the answer for your question, too.

CO2 addition will obviously increase the growth rate of the plants (and therefore the accumulation of allelochemicals in the soil will be faster, and more likely to outstrip the rate that bacteria would break them down). Do you folks who supplement CO2 also dose fertilizers to the water column? And if so, is the water column dosing more or less in proportion to your CO2 addition? Bpimm says they don't add large amounts of CO2, but what about fertilization rates? It seems to me, being a casual observer of the high-tech method, that the trend is for ever increasing levels of CO2 and Ferts (they usually seem to go hand in hand). 

Also, those of you adding CO2 to a soil substrate tank, are you using a DIY, or pressurized system? My thought is this - with DIY, it seems that the CO2 levels are more variable as the yeast concoction ages, and I'm wondering if the levels of CO2 addition are on the low side anyhow, I'd imagine that the tank might be more resiliant to these fluctuations. Or, is it the opposite - at lower levels of CO2 addition, consistency is paramount in order to see the results?

I recall its been brought up that the soil substrate could possibly become exhausted faster if everything was ramped up (ie, CO2 addition, fert addition, etc.). Have any of you adding CO2 experienced this?

Thanks in advance for your input.
-Jane


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## bpimm (Jun 12, 2006)

Jane in Upton said:


> I have a question for those of you adding some CO2. I don't mean to hijack your thread racialfish, but it's part of the answer for your question, too.
> 
> CO2 addition will obviously increase the growth rate of the plants (and therefore the accumulation of allelochemicals in the soil will be faster, and more likely to outstrip the rate that bacteria would break them down). Do you folks who supplement CO2 also dose fertilizers to the water column? And if so, is the water column dosing more or less in proportion to your CO2 addition? Bpimm says they don't add large amounts of CO2, but what about fertilization rates? It seems to me, being a casual observer of the high-tech method, that the trend is for ever increasing levels of CO2 and Ferts (they usually seem to go hand in hand).


Jane, I have pressure CO2 on 3 tanks and none on 2 tanks and no dosing of anything else. if I have a decency I try to add the element into the soil.
The trend for ever increasing levels is something you see in every aspect of hobbies, there is always someone who tries to push it farther than everyone else, I guess it is just the competitive human nature.



> Also, those of you adding CO2 to a soil substrate tank, are you using a DIY, or pressurized system? My thought is this - with DIY, it seems that the CO2 levels are more variable as the yeast concoction ages, and I'm wondering if the levels of CO2 addition are on the low side anyhow, I'd imagine that the tank might be more resiliant to these fluctuations. Or, is it the opposite - at lower levels of CO2 addition, consistency is paramount in order to see the results?
> 
> I recall its been brought up that the soil substrate could possibly become exhausted faster if everything was ramped up (ie, CO2 addition, fert addition, etc.). Have any of you adding CO2 experienced this?
> 
> ...


I have never tried DIY CO2 it just seems like a hassle. I have to belive that the substrate will have a shorter life if you add CO2, that is one of the reasons I add a smaller amount of CO2 than most. I am trying to just keep CO2 available and stable not deplete it. In nature there is alot more water volume and surface area per plant than in the aquarium therefore I think the CO2 levels in nature would be more stable, as a general rule, I'm sure there are cases that wouldn't follow this theory.

as for the allelochemicals I don't have a tank that has been running long enough to test this theory, and how would we know if it was allelochemicals or just the substrate being exhausted? without a lab to test the substrate I'm not sure we can answer this question.

About 10 years ago I had a soil tank with CO2 and after about 1.5-2 years the growth slowed and the tank fell apart. I had to start over with new substrate. I have to believe that the substrate has a finite life with added CO2 but I don't know the definite cause.

I look at it as incentive to try a new tank layout. 

Brian


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## AaronT (Apr 26, 2004)

I am using pressurized CO2 on all of my tanks. Two of my soil tanks have lots of stem plants and I've been dosing small amounts of potassium. Other than that I might dose excel just to add a little extra carbon insurance. 

I did setup my soil tanks a little differently than the walstad method though. I added natural clay to the soil to add iron and help bind nutrients better.


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## Jane in Upton (Aug 10, 2005)

Interesting!

Yes, Brian, on the allelochemical buildup, I agree with you - who knows if its allelochemicals, or soil exhaustion? I just wanted to clarify that the faster allelochemical bulidup was related to the plant growth, not directly linked to the CO2 itself, for racialfish. 

The whole hassle idea is why I still don't do CO2- if I did, I'd spring for the pressurized system, and don't have the budget for it at the moment. 

I just re-did my 30 gal, and added a small amount of laterite into the soil as an insurance against iron deficiency. I forgot to add the usual 1 Tbsp/sq ft of ooidic (CaCO3) sand I use (DOH!) but oh well. 

So Aaron, what was the source of your natural clay? I used to run two kitty litter substrate tanks, a la Quackenbush. I'd just set them up when I discovered the El Natural forum, and read the Walstad book, thereby becoming a soil underlayer convert, LOL! The 30 gal was one that did remarkably well for 2+ years, and I've also just broken down the 20H, which wasn't as versitile, but did OK with Crypts, Echinodorus, Aponogeteons and hairgrass. I picked up some raw pottery clay, the very red stuff, with the thought that I might use it like the old Duplarit K balls as a supplement, if necessary. So what natural clay did you use? And at what proportion in the soil?

Oh, and Brian, are all your tanks, both pressurized CO2 and non-CO2 tanks with soil underlayers? Your reasoning on the volume of water, and therefore CO2 equilibrium makes complete sense.

-Jane


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## bpimm (Jun 12, 2006)

Yes, all of them except my daughters 12 Gal Eclipse, I haven't got to it yet.  

80 Gal, Pressure CO2, continuous water change.

30 Gal, Grow out, bare bottom, with plants in pots. Pressure CO2, continuous water change.

29 Gal, continuous water change. no CO2

25 Gal, full El Natural. no WC, no CO2.

20 Gal, Grow out, bare bottom, with plants in pots. Pressure CO2, continuous water change.

14 Gal Hex, Pressure CO2, continuous water change.

12 Gal Eclipse Gravel with potted plants, no WC, no CO2.

2 Gal hex, Pressure CO2, continuous water change.

3 Vases, no WC, no CO2.

All of them have soil under gravel substrates including the potted plants.


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## essabee (Oct 11, 2006)

Go ahead and add CO2, just don't overdo it or your plants would look like they are on steroids and you will be forever forced to feeding them.

It is quite natural for plants to need extra CO2 in even a plant and fish aquarium. In natural water-bodies you will find the plants in patches and vast spaces of deep non-plant areas. The water currents, set up by flows, temperature or wind, bring the CO2 laden water to the planted area and so the CO2 starvation in natural water bodies would be less. Again the extra surface area would allow more CO2 to get added so would the large area of the substrate covered with debris. 

The only difference you would have is your aquarium water is going to be richer in CO2 than the water of natural water body. This will reduce the ph of your aquarium water. As long as you keep the CO2 addition low this will not be a trouble unless you’re already have low ph (range on the lower side of the requirement of the aquarium inmates) or very soft water (then you will be forced to increase temporary hardness).

As far as I am concerned your aquarium will still be a natural aquarium.


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## Jane in Upton (Aug 10, 2005)

Wow, Brian, that's a lot of tanks! I feel much less self-indulgent now, LOL! Also, I can keep this in mind to justify getting another at some point!

I also have a bare bottom grow out tank w/ plants in pots. 

Yes, the idea that in larger bodies of water the bare areas allocation of CO2 would be somewhat available to the more densly growing areas makes sense. 

I agree, if the dosing of CO2 was low enough not to make routing fertilizing necessary, I also would still consider it "El Natural".

-Jane


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## Satirica (Feb 13, 2005)

> Go ahead and add CO2, just don't overdo it or your plants would look like they are on steroids and you will be forever forced to feeding them.


Not true. Excess CO2 does not cause a problem. You can add CO2 to a tank with minimal nutrients and see healthy growth. It is only when light levels are greatly increased that you must provide a lot of ferts.


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## essabee (Oct 11, 2006)

I dont think it is the lights alone, Liz. I think it is the entire spiral of Lights+Ferts+CO2 going up and up which creates the steroid effect, and that is exactly what I meant, and in the context should have been clear. Sorry if I gave a wrong impression.


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## Satirica (Feb 13, 2005)

Thanks for clarifying -- that I agree with. I've seen people get started pushing one then the next then the next when the variables are CO2, light and ferts. 

If you have high light you must use CO2 or Excel or something. WIth CO2 you don't need high light or high ferts. And I don't know why you'd need high ferts without CO2 or high light but I've seen people do that, too.


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## sb483 (May 29, 2006)

Satirica said:


> If you have high light you must use CO2 or Excel or something. WIth CO2 you don't need high light or high ferts. And I don't know why you'd need high ferts without CO2 or high light but I've seen people do that, too.


I don't agree with that. All my tanks get direct sunlight for a large part of the day, but I don't use CO2 or fertilizers (aside from fish food). In Diana's book it says tanks with CO2 have very rapid growth rates and so might require extra fertilization - the opposite might be true, that if you use CO2 then you should probably use ferts.


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## Satirica (Feb 13, 2005)

I doubt that your tanks are getting the equivalent of 3 - 4 wpg of T5 or CF lights for 10 hours a day. That is high light. Without CO2 or Excel, those tanks become algae pits quickly.


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## DataGuru (Mar 11, 2005)

My 125 isn't. It's sitting in front of two south windows and gets direct sunlight for multiple hours per day. It also has 180 watts over it for like 12 hours per day.


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## essabee (Oct 11, 2006)

Actually there is no 'must' for CO2 if your lights are high. All that can happen is the submersed plants will have very little CO2 for use in photosynthesis, but they will continue to get CO2 from the fishes and by diffussion from the atmosphere.

Even when CO2 and Lights are high there is no 'must' for Nutrients. The plant growth will be restricted to the level of the nutrients available.

The problem of 'must' starts when your nutrients are high. Plant growth is required to stop alga attacks and water detoriations. Lights or CO2 or both may become 'must' if they are the limiting factors or sponge out the nutrients using floating plants.

This is exactly why we start with a substrate which will not add too much nutrient. That is why the advice to DIY aquarist is of kitty litters, potting soil, and the 'of the shelf' aquarist go for the ready made soil mixtures, and all aquarist make the endless debates.


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## sb483 (May 29, 2006)

Satirica said:


> I doubt that your tanks are getting the equivalent of 3 - 4 wpg of T5 or CF lights for 10 hours a day. That is high light. Without CO2 or Excel, those tanks become algae pits quickly.


My tanks are all in front of windows, getting direct sunlight, some for the whole morning and some for the entire day. I can't compare wpg but sunlight is pretty strong. I don't use CO2 or Excel, but I have growing plants and no algae pits (though thread algae does seem to show up with direct sunlight, and I have to pull the strands out).


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