I would start with label directions and see if the plants recover, or start growing normally. If the response is slow, dose a bit more.
It is pretty hard to OD on potassium, so going with more is just fine. (This is probably the first one I would add more of, above the labeled dose)
Plants need phosphorus, but in such small amounts (compared to the N and K) that I would add more only after adjusting the others.
Plants use a lot of N, but fish food supplies quite a bit. What does you NO3 test show? If it is always reading 0 ppm, then you will need full dosing of nitrogen. If the fish food is supplying some nitrogen (for example, if the test usually reads from about 1 to 10 ppm) then you would need less.
Flourish Trace is fairly low in micros, perhaps switch to Comprehensive.
Once you get close to the right fertilizer dosing you might find the plants use more CO2, also.
If you want to try EI, using the liquid ferts, you can, but it is more expensive. However, dose at the maximum rate on the label, and do a 50% water change once a week. As you get a feel for how your plants are responding you might be able to adjust the dosing, perhaps do smaller water changes.
Only change one thing at a time and see what the results are. That way you know the cause and effect.