Hello everyone
I am not worried about CO2, it is in the title non CO2 tank, you just have to go with the flow it slowly growing tank and it always will be, that's the beauty of it, low maintenance, plants stay nice for longer same size no need for constant trimming. Once the tank is established it is very stable environment with no hassles, no algae etc. The CO2 is there, it come from fish, plants at the night time and surface movement.
If you want bust your CO2 just do DIY CO2 that will bring the CO2 higher but not too much, it will be big difference to it, and don't worry about fluctuations of CO2 as long you periodically refill the bottle and don't increase you light and you have the right temperature.
I had low tech tanks for ever(mostly for breeding fish), in my low tech tank I don't use liquid CO2, low light up 8 hours, 23'C, tab water, quite small internal filter, lean fertilizing and gravel no soil, but I have been adding some tropica tablets recently, up to now I wasn't, just fish waste and I believe big part of success in this are snails red-rimmed melania they are helping with oxidation in the gravel for bacteria and movements in there and I don't siphon the gravel at all(I know sounds mad) I have plants rated medium such as Monte Carlo, rotala, super red mini and rotala wallichii rated advance, I am not saying that the plant are thriving in its best, but they are growing slowly and healthy, even my rotalas are getting bushy after trim 2-3 stems coming out of one stem. Anubias, buce are flowering regularly. I don't want to spam it here with my photos for visual "prove". There are some photos of the low tech tank on Instagram @jozef.sc but if you are interested I can put some here. It fully planted tank with no more space for plant so I guess the amount of plant mass is not the issue, I would say more the better.
I have learn from old school guys to don't put crypts and vallesneria to the same tank as each plant is changing the environment to its own standards and one doesn't like the other, depends which plant is stronger in the tank, or if there is balance or big volume of water then can be doable. Please don't quote me on this one, I have never used both together, so non experience with it.
Regards
Joe