definitely for your situation, chemical treatment was necessary as the shear size of the tank makes normal % WC impractical. I recommend having floaters or some kind of plants to absorb the nitrates more naturally as you want to strike that balance where the tank will take care of itself, or so to speak...
there is another ammonia detoxifier which also nullifies toxic metals for ponds. i came across this at petco the other week but didnt catch the name. im glad to read your success here.