Dead snails would do it especially it it were a lot of them. And if the tank is fairly new, there could have been an ammonia spike well ahead of the high nitrates as the bacteria were playing catchup to the new load. That is a lot more likely to cause death than even 80 ppm of nitrate. How old is the tank?No I do not have a sump, I have a canister filter. And you may be right about something rotten in the tank. It may be snails because I started noticing the nitrate when I saw empty snail shells.
2 cleaner shrimp died, want to rock flower anemone, A tomato clown fish and snails



