That link Swisscheesehead gave was a really good read even if it did not contain any definitive answers.
It seems, by looking the Hoppy's graph, that in low light setup, the plant growth varies dramatically even with small co2 changes when the concentration is less than 10 ppm. And I am going to guess that fluctuation leads to problems with plants and that in turn leads to algae bloom. And that same 10ppm is also the upper limit that Tom Barr suggested for optimal algae growth. So based on these, I think that I will aim to CO2 at 10-15ppm when lights go off. So then CO2 is not the limiting factor and fluctuations should not affect the plant growth. And I should have good flow with over 10x the tank volume per hour so the concentration should be fairly even. I just need to keep lights low.
I believe also in high tech tanks many have gotten rid of algae problems after pushing the CO2 past the 30ppm mark that was the point where CO2 changes stopped affecting plant growth in Hoppy's graph. That would support my "theory" also.
Or that I do what Swisscheesekake is doing and add so trivial CO2 that it helps the plants some, but is always so little that plants know how to build their "production lines". So no fluctuations between having limiting and unlimiting CO2.
Last edited by Darkblade48; 12-02-2016 at 10:46 AM.
Reason: Please use the edit function for back to back posts to keep threads cleaner