Emergency My Fish Are Dying Help!"

[Dlynn87]

Hi all I am new to this forum. I have a 20 gallon fish tank with 5 glofish, 2 platys a African frog and a pleco. Had the tank for 4 weeks now. Last week bought 2 platys and a glofish. Yesterday frog died,today pleco died. What is going on? Took water sample to Petsmart before adding any fish initially said OK to start adding fish. Always put fish in bag in tank before adding them for at least 30 minutes. Did add pet smart water, could that be my problem as everyone was healthy until I added the last set of fish last week. I dunno, new fish keeper. Going today to get a water sample and test kit. Any suggestions on the better water test kit I should get? Thanks for helping in advance. I will post water results a little later once I get them. Don't want anymore fish to die.