Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Plants need over a dozen elements to live.
Some are in the water: Hydrogen, Oxygen, perhaps Ca, Mg (if the GH is over about 3 German degrees of hardness the Ca and Mg might be OK)
Some can be added as fish food, but if you are running a high tech tank (CO2, good light) fish food is not enough. Fish food is reasonably high in N, P and most traces (enough for a low tech tank), but is low in K, Fe, Ca and Mg.
Flourish Comprehensive is mostly traces. You are getting traces from fish food. Don't over dose.
I would never suggest adding more of what the plants use so little of (trace minerals) before making sure the elements they need more of are taken care of. (N, P, K)
it really comes down to 2 systems:
If you have high light and CO2, then assume fish food is not enough, and follow a full dosing schedule such as EI or PPS-pro.
If you have low light and no CO2 then assume fish food is supplying N, P, and most traces, but you still need to dose K and Fe. Check the water for Ca and Mg, and dose GH booster if needed.