@mngrif Ahh yes fully aquatic plants absolutely need injected co2 in the light phase, I see why you said that now. terrestrial plants are different sorta.

With all plants (or anything in general) if it produces energy from light then it consumes CO2 to do it (as you know) and if it consumes its energy (sugar) instead of light then it consumes O2. so during the light phase it consumes CO2 and dark phase O2.

But thats an oversimplification. In reality the sections of a plant that produce the sugars (any part that is green) will consume CO2 when light is present. But since the roots 24/7 consume sugar and do not produce their own energy all roots of all plants need O2 and not CO2.

Since an aquatic plant has its whole system underwater whent he light is on it needs more CO2 overall than O2, when the lights are off it needs O2 only. But since terrestrial plants have their leaves out of water and the roots in water they would 24/7 need oxygen only injected into the water. The need for the CO2 int he green leafy parts would obviously come from the air.

So at least in that sense they may be a bit easier to care for than traditional aquatic plants.