I have a 70g tall tank with exclusively lake tanganyikans. It has been set up for over 7 months and very stable other than routinely high nitrates (probably from not enough water changes). I went out of town for 2 nights and my fish sitter over fed the tank, visible food material on the bottom from the day before! One adult trewavase was dead when I got home yesterday, so I did a 30% water change last night. Today I got home and two more small fish dead, a caudopunctatus and a goby cichlid
, and everyone else is breathing VERY RAPID, mostly sitting on the bottom of the tank, kinda lethargic. My ammonia and nitrite are both 0, no phosphates, high nitrates (but that's nothing new). pH 7.8 and temp 80 degrees, I have added some cichlid trace elements, cichlid salt, Prime, and a little tanganyikan pH buffer, any suggestions??????