about to give up

[onyx]

I don't know why I am having so many problems keeping these fish. I have 5 of them, and nothing but problems. One has pop eye, one has fungus on its fin, one has just gotten out of quarantine due to slime coat issues, and now one is laying on its side probably dying. I test my water daily. I do water changes often. I am so confused. My other fish are fine. Please help me.