What freshwater fish have you had success with?

All kinds of Ornamental Goldfish. True. They’re a little messy at times. But they are a very nice, relatively forgiving fish that can help you improve your fishcare skills. They can really develop into quite the affectionate fish if you (as their keeper) are good enough.

I’ve also kept a wide variety of others.
What kind of fish do you currently have left in your tank?
This usually makes a big difference as to what we can wisely suggest to you.

Edit: I’m sorry to hear your fish have begun to die off.
I’d carefully research the kind of schooling fish you have and for every fish that dies off get more of them ONLY if you feel you still have room left in your tank.
It’s always a good idea to base your tank off on a nice type of schooling fish. (in the biggest & most visible possible school)
Fish feel at their most comfortable in a big school.

I know some will disagree but I adore Guppies. I’ve had a successful group of guppies that have lasted many years, but it’s not the individual lives, it’s their continous breeding and replenishing. If your looking for a long living fish, I had real good luck with bleeding heart tetras. I had a pair last about 5 years, same with my algae eater. The tetras can be a little bossy but nothing severe.