aquarium fish dying in a ten gallon tank, betta, mollie, platie?

[Lauren D]

I have a ten gallon aquarium. I started it by letting the water cycle for a little over a day, then a put a crowntail betta in. After a few days, I put in four marble mollies. They all seemed to be doing fine, but a few days later one of the mollies died. I never saw him looking lethargic or anything. About a day after that, I went and got two mickey mouse platies. They seemed to be doing well too, but then one of the platies died! A couple days later, all the fish seem to be doing fine- swimming, eating, not bossing each other around, but then my betta dies! What could be wrong?

[FishMomma]

See my other post in the duplicate thread.

[BettaLu&Meg]

Dupilcate thread!