its not what you feed...as already said all food has no3 and po4....its how you feed
if your feeding frozen food cubes, after thawing rinse them in ro water this will cut down these levels dramatically, also only feed what your fish can eat
You need to let know what kind of maine fish your talking about because they allot of them out there and they all have there own likes.
And just so you know all foods will raise nitrate and phosphate levels if your not care full and have a good filter system
