About a month and a half ago I bought a 10 gallon aquarium kit for tropical fish. I started out with some guppies, some bala sharks, a dwarf gouramie, and two red platys. I know I went a little overboard on the amount of fish, I was overzealous. Within the first few days I lost two guppies (probably a result of stress, they tested the water at the store and it was balanced fine). I had the rest for several weeks then within a week I lost almost all the fish except one guppie and two gouramies. I did replace some fish, but every fish I bought as a replacement died. If I didn't still have three of my original fish, I would be lead to believe there was something wrong with the water or the food (they're getting tropical fish flakes as well as brine shrimp). The fish I still have are doing extremely well. I have a 55 gallon tank that I want to set up and move those fish into and get a few more but first I want to resolve why I kept losing fish. Should I buy a ph test kit? Should I be using anything to treat the water besides just some basic water treatment? Should I try some other supplements besides what I'm feeding? Also if I do upgrade to the bigger tank, any input on what sort of fish I may want to look into? Any insight would be helpful. Thanks.