My boyfriend and I have tropical fish and have done so for over a year. We had to get a new tank as our old one was leaking we swapped all the fish over and also got some new ones. since we have had this tank we have had nothing but problems, we cleaned this tank out properly and have to what we know done everything right. yesterday we got some new fish and all where dead within 7hours! the shop was happy to swap the fish over today and already 3 have died within a couple of hours with one more that seems to be on its way out! I dont understand what we are doing wrong or if there is a problem with the tank? can anyone help us?? thanks!