u/InspectorDue9323

Hi everyone on this subreddit. I was looking for some advice about aquatics. My store has a sunp that keeps killing fish. We've tested it so many times, nothing is wrong. We've put in bubblers, adjusted the temps, and a bunch of other things, but it doesn't work. Everytime we put fish in they die within a couple days or even a couple hours. I have no idea what is wrong with it or what else to do. Does anyone else have a sump like this or any advice, I don't know what to do

Edit: we already tried going through official work tickets but we don't have an animal manager right now and the aquatics helpline has always said it's somehow our fault because we're doing something wrong, so we gave up with asking them for help