Albino Tiger Oscar Behaviour ?

I've got two new albino oscars and for the first couple of weeks everything
was peachy. I put a power head in for a bit and found that one of them
didn't like it so I removed it and it seemed to go back to being okay. The
last couple of days one of them has been acting slow and listing to the
side a little. I've checked nitrites and ammonia and both are virtually
zero. temp is 80-82. They're alone in a 25'ish tank, they've got a rock
cave, some plants, and I feed them feeder guppies and dried shrimp pellets
(sinking).
Any ideas?

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