The nitrates and ammonia were acceptable. I did weekly water changes (~25 of the tank). I let the tank establish for about two weeks before adding the fish the last time (Goldfish try). With the platties I let it establish for a week.

I tried 3 platties and I tried 2 gold fish (these were on two separate tries). The water I used is from the town.

I bought the appropriate food for each fish as well when I tried the different breeds. So I'm not trying to give them something inappropriate.

Before the fish died, each one was lethargic, tending to hide in the fixtures and not bothering to eat. Usually the next day or so I found it dead on the tank bottom or stuck next to the intake for the filter. Hence my thought that maybe the filter pump was too powerful for the tank. The pump/filter I have is linked below. I got mine at Petco.

I had heard that I may want to try and hide the filter intake behind some scenery to prevent the fish from getting sucked towards it. Would you agree?

I miss the goldfish I had when I was a kid. It swam in a glass bowl with marbles on the bottom and was frickin' indestructible. He lived for 8 years.