Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
If the fish food is giving you enough nitrogen (based on the nitrate test) then it may also be giving you enough phosphorus, but probably not enough potassium. Probably getting enough traces, except for iron.
You might cut back the EI and try it more like this:
Little or no KNO3
Little or no KH2PO4
Use K2SO4 instead, at whatever rate is suggested for the KNO3.
for example, if the chart suggests 1/4 tsp of KNO3 and you think 1/8 is enough, then dose 1/8 tsp K2SO4 so the plants still get the potassium they need.
Little or no trace.
Dose chelated iron instead of trace, or combined with the trace minerals so the tank is getting more iron and less trace minerals.
When I was running heavily stocked tanks all I needed to dose was K and Fe. Fish food had everything else, water changes kept the GH and KH correct. As I improved conditions (light, carbon from excel) I had to start adding a little bit of other things, but kept the K and Fe dosing the highest, since fish food was still supplying a lot, just not quite enough N, P, traces.