When the nitrites initially spiked, it was darker than the 5.0 reading- I have the API test kit. My 55gal tank is stocked with 2 angelfish, 2 giant danios, 2 julii cory catfish, 1 dwarf blue gourami, And 1 small bristle nose pleco. I have lost 1 cory catfish- I started with 3, but so far all the...