Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish foods have most, but not all the nutrients that plants need if you are running a reasonable stocking rate, and a low tech tank.
It is low in K, Fe and Ca. You will probably also need to supplement C.
In a high tech tank (yours) fish food should not be counted on to supply enough of all the things plants need.
I would at the very least supplement K, Fe and C (I see you are adding C- drop checker yellow).
The water should supply enough Ca and Mg if the GH is >3 degrees. If you are using mostly RO, then add GH booster to 3 German degrees of hardness.
You can use the NO3 test as a stand in for P and traces. However much NO3 you dose, then dose the right ratios of P and traces according to whatever method you are following.
If you are doing the fishless cycle, then you can work around the dosing and see what works. You should not need to dose any N during the cycle because the plants will be using some of the ammonia as a source of nitrogen. But they will need the other things.