my levels were always at a 40 for the last year in a fish only tank, i was fine with that. the tank is a 135 gallon fish only with cuc. i have 1 yellow 2 clowns (false) and now added 3 green chromis two weeks ago,prior to this added 3 more chromis smaller one two got suck up into the wet dry,removed them the next day, one was lost, i found him yesterday while on did my maint. i am guessing this was the reason for the spike up to 100. i did a 30 gallon water change plus cleaned the bio balls using tank water, all fish are doing great eating swimming, but levels are still at 100, going to do another water change 10 gallons today, no live rock, only fake corals all my other readings a great 0 amm 0 nitrites temp 76 sal 1021