Frustrating isn't it. Don't panic, just think in horse terms. Check the paddock (tank), feed (overfeeding causes laminitis, foundering or bizarre behaviour, colic etc. fish die), etc. :lol:
I had a bad run with fish stressing and dieing and the more things i tried the more they stressed out. I stopped and pretended they were my horses. Eventually worked it out, but damn its hard when your new and don't know what to look for.
Good luck. Sorry no real practical advice but i'm new to this too. Ask me a horse question and i can help you. :lol: