What was the previous owner feeding them?

I would also recommend a Mela & Pima fix combo to treat any bacterial or fungal infections they may have. It wouldn't hurt any of them that don't have anything wrong with them physically. However, I would make sure that your water quality is impeccable. Most illnesses are water quality related. The bad news is if your fish aren't eating that's not a good sign. There's nothing you can do but try to get them to eat anything.
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Phishie
Site Coordinator

"An ounce of prevention is worth a pound of cure."