Canister filters are known to create lots of nitrates...
Well, do you want the ammonia to stay as ammonia? Does not matter what kind of filter there is on the tank. If you add nitrogen as protein it will go through the nitrogen cycle and end up as nitrate. Good thing, too. The intermediate steps (ammonia and nitrite) are toxic.
If the NO3 is a true reading, and it is coming from fish food (at least the 40-80 ppm is probably from fish food) then fish food also supplies:
N, P but not K
Somewhat lacking in Ca
Low Fe, but OK for the other trace minerals.
So, count the fish food as fertilizer, and reduce the other fertilizers where fish food is a good supply.
If you get such high nitrates from fish food, then you can assume the phosphate and traces (except for iron) are good, too.
If the GH of the water is at least 3 degrees, then assume the Ca and Mg are OK, too.
More and larger water changes.
Callibrate the NO3 tests.
Adjust ferts to account for the fact that you are already adding ferts in the form of fish food. Probably just dose K and Fe.
When you get the CO2 squared away the plants may start using the fish food more effectively, so monitor the levels with whatever tests you have.