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.