I set up a new tropical tank on Sunday and have already lost 5 fish!! The angels were the first to except except for one! This morning I found a dead silver shark and a new plattie that I only put in there yesterday! PH is 7.8. How can I prevent more deaths? None of the little tiger or green mossy barbs seem bothered by it???

What are your water parameters? (Ammonia, nitrate, nitrite, hardness, total alkalinity, temperature).