Adverse effects from injecting CO2 into substrate? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 01-29-2012, 02:22 AM Thread Starter
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Adverse effects from injecting CO2 into substrate?

I was considering trying a new manner of injecting CO2, which is into the substrate. Would this cause any adverse effects or unanticipated changes to the substrate's chemistry?
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post #2 of 6 (permalink) Old 01-29-2012, 02:24 AM
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I dont know if it would hurt anything but dont really see it being dissolved into the water column that well since there isnt much flow if any at all in the substrate. I would think that the bubble would just accumulate until they finally broke free of the substrate and floated to the surface wasting the CO2.

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post #3 of 6 (permalink) Old 01-29-2012, 02:48 AM Thread Starter
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I note that there are a few species of aquatic plants known to draw in CO2 from their roots. And there are perhaps others that can as well. Many rosette plants in particular have strong root systems, and will oxygen into the substrate around their roots. We believe this is to protect their roots, but there is also the possibility that they are cultivating other nutrients for themselves as well, by supplying oxygen to the bacteria in the sediment surrounding their roots to allow them the break down nutrients with the benefit that they'll release CO2 while doing so.In this manner aquatic plants MAY happen to 'farm' their own CO2 supplies. I'm not sure if it actually works like that on a widespread basis, but I thought I might want to try it out on a trial basis to see if it might look like it has some benefit to. If it did work then I could use a lot less CO2 as I wouldn't have to worry about if off-gassing or whether my surface agitation was too strong.

To accomplish this I'd have a series of small perforated tubes running under the substrate. And I'd wrap this tube in a foam, and have a very small water pump circulating water through these tubes continually as a closed circuit. I could also dripfeed nutrients into this circuit, perhaps via a small dosing pump, in case the plants appear to need extra nutrients. I'd top this tubing manifold with an inch of mineralized topsoil, and then an inch of sand. The circuit could run through a CO2 reaction chamber, which would therefore show whether all the CO2 being injected is being absorbed, and therefore should be cycling fully CO2 saturated water. (I wouldn't be running CO2 in gaseous form through the substrate tubes).

And hopefully, the plants would then extend roots into the foam which should be saturated with CO2 and nutrients. Perhaps the flow through this circuit would induce a tiny bit of flow through the substrate as well, and prevent the drawbacks of allelopathy, similar to how substrate heating coils were supposedly, (but unsuccessfully), meant to work. Preferably, the nutrients and the CO2 would stay primarily within the circuit and the foam instead of leaching too much into the substrate.

Another purpose in doing this would be to try to keep the water column clear to some extent of nutrients, so that those nutrients and nitrates aren't detrimental to the fish. And as algae lacks roots, it might be entirely disadvantaged as it can't reach the nutrients and there might be a limited amount in the water. I intend to use some hardy floating plants or terrestrial plants to strip whatever nutrients there might be in the water as well. But the aquatic rooted plants should in any case not be nutrient limited at all, even if the water column happened to be free of nutrients.

Even if the CO2 in the substrate proves to be a bad idea, I'd want to install the manifolds for the other nutrients anyway. I may not need to use the manifolds initially, but if the plants after some time start showing deficiencies when the MTS gets exhausted then I could recharge it in this manner. As I'd in any case be using CO2, I expect the potentially rapid growth would deplete the substrate eventually. And as I'd intend to use this approach for quite a big heavily planted tank I wouldn't want to be trying to stick root tabs under each and every plant including under dense carpet plants. I'd prefer a system which could more consistently and directly enrich essentially the entire substrate footprint continuously.

So, might this work decently or would that cause some manner of unforeseen problems? I appreciate it's a slightly complicated weird way of doing things, but I see it as a hybrid between the low-tech and high-tech approach to try to overcome the drawbacks of each.
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post #4 of 6 (permalink) Old 01-29-2012, 09:12 AM
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Thats an interesting concept Mxx. C02 is commonly injected into Hydroponic systems. In hydroponics, nutrient enriched water is pumped so it passes through the dangling roots in a continual loop. The amount of C02 they inject is very little compared to what we do in an aquarium, typically 2 or 3 bubbles per MINUTE.

I don't know how you would disperse the C02 in the substrate Ben, so it would be even throughout the entire substrate. Simply injecting it at a given spot would not cover much of an area. If you had a current of water moving across the bottom of the substrate then that might work. Either the gas would have to come into direct contact with the roots, or water carrying C02 would have to pass through all the roots.

All rooted plants in the substrate actually have photosynthesis at the roots giving off both oxygen and C02, as well as intaking. Even bacteria in the substrate does this. It would be interesting to see experiments involving substrate injection. Try it out!

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post #5 of 6 (permalink) Old 01-30-2012, 12:15 AM Thread Starter
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Bizarre. I wouldn't have expected that terrestrial plants would have benefited from having their roots exposed to CO2, being that they have so much easier a time getting CO2 from the air than aquatic plants have from getting it underwater.

Do you happen to know what crops they grow like that? I tried googling it briefly, and came up with mainly a lot of links for growing cannabis which I decided not to follow... But considering the characters I met the last time I was in Salem, there accordingly may be a fair bit of local experience with hydroponics that you may hear about even!

In any case, that's roughly the idea, to grow aquatic plants with hydroponic tubes, while they're are... underwater.

I'm thought that running small diameter slightly perforated tubing in a circuit around the bottom, with the tubing say 2 or 3 inches apart would cover enough of the substrate area that most of the plants could spread roots to reach it. (Or you might instead end up with your carpet plants growing instead in neat little rows?) With a thin layer of foam wrapping the pipes hopefully that should more or less keep the co2 and nutrients contained within the 'hydroponic' tubes and surrounding foam, but the plants should be able to penetrate roots through the foam to tap into the enriched zone within.

Another idea could have been to stick in some undergravel filter plates, and perhaps cover that with a thin layer of soft foam to try to keep out some detritus and debris. But instead of using the plates as an undergravel filter, you could cycle co2 and nutrient saturated water throughout this plenum zone, and the plants should be able to find the holes in the plates to tap feeder roots through as well?

I'm not sure which system might better accomplish what I was considering.

I've never heard anything about photosynthesis occurring at the roots and co2 being given off there. Do you have any links to where I could read more about this? I'm familiar with bacteria giving off CO2 though of course.

There is perhaps enough indication that this could possibly work with plants that I'd like to at least try it. I was just wondering whether anyone might know of any possible adverse effects or reactions that could result from a lot of CO2 in the substrate, (despite that that's not even an unusual thing to have in nature). And if there were concerns then perhaps I'd be able to find ways to safeguard against those. Being that I'd plan to use this with MTS adds another variable to the matter though.

Unfortunately I wouldn't however have a control group to measure against, so it's not exactly a very critical experiment. But if I have robust plant growth then that should be sign enough in itself I guess.
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post #6 of 6 (permalink) Old 01-30-2012, 02:41 AM
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Injecting CO2 into hydroponic systems may have more to do with keeping a slightly acidic pH than with actual uptake of CO2.

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