Try Excell for carbon, not CO2 injection
If you insist on having an airstone, then you could try Seachem Excell for carbon.
But, really, if you have good lights, and CO2 but not too high, and reasonable fertilization, the plants ought to be making lots of O2.
Too heavy a fish load plus too many plants could lead to low O2 by morning. Fish damaged by high ammonia during initial cycle may be overly sensitive.