Would any additives benefit the plants since I will not be using CO2?
Floating plants use co2 from the atmosphere so injecting it would be pointless. Depending on your plant bioload id say no, you might not need to add fertz. On the other hand it would help the plants grow faster. If you were to dose something I think the most important flourish product is flourish comprehensive as it has both some micro-nutrients, and more importantly iron. Macronitrients shouldnt need to be dosed provided you have messy fish or overfeed. But pottasium is a macro and it is not found in food so that too.
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