Might have triggered breeding mode.
One day I changed the water in my red devil tank, dropped some frozen krill in immediately after and he started humping the glass. He had his wiener out and was going to town. It went on for about an hour.
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I think you lack an understanding of how fish breed.
It could be the beginning stages of Ich. at first the fish will seem to scratch against stuff, then the white dots show up, if this happens all you have to do is go to the pet store and get some treatment. and follow the instructions