dying fish

I received a 5 gallon aquarium as a Christmas Gift. I have had the tank going for about 10 days. I am having a terrible time with fish. The most fish I had at any one time is 6 . Zebra Danios, Pearl Danios, Cory Catfish. Everything died except one Zebra. I have a filter and airstone in the tank...

Hey all, new to this forum malarkey so please be gentle! Ok so the short and tall of it is I got my first aquarium (fluval edge 46l) and up until recently all was well, I changed the water (all of it which was probably a bad idea..) but all the fish seemed happy. Had 3 neon tetras, a plec, a...