One possibility, seal the lid on the tank tightly and a high concentration of CO2 will build up in the air in the tank which will lead to more CO2 being dissolved in the water due to the increased partial pressure of CO2 in the tank’s atmosphere.
Another choice would be to try to push the already dissolved CO2 to dissociate by supplying calcium ions to pull bicarbonate ions out of solution (by association, the calcium bicarbonate is still dissolved however). What happens is CO2 gas is hydrated, becoming carbonic acid H2CO3 which dissociates into HCO3- (bicarbonate ion) and an H+. A Ca++ ion associates with 2 of the bicarbonate ions Ca(HCO3)2 forming Calcium bicarbonate. If there is any ammonia being released to the water via respiration of fish or bacteria the NH3 molecule hydrates to become ammonium ion NH4+ and an OH- ion. The H+ above and the OH- here reform as water and our plants happily use the NH4+.
So by driving the CO2 into Calcium bicarbonate you are drawing more CO2 into the water. If the plants begin to pull more CO2 out of the water than the tank atmosphere can supply, the bicarbonate ion can reverse the process to become CA and carbonic acid which will reform CO2 and be used by the plants. Or in some instances, a plant can use the Ca(HCO3)2 and take out a CO2 and leave an CaHCO3 Calcium carbonate molecule which will settle out of solution.
Anyhow, while the waterfall is degassing dissolved CO2, or absorbing CO2 from the enclosed atmosphere, it won’t degas bicarbonate ions.
Aquascape? I'm a crypt farmer.
It's a fine line between fishing and standing on the shore looking like an idiot.
That IS an aquascape, it's titled "The Vacant Lot".