Yes. Ok, I've figured it out, but now I have a new problem.
He has finrot. I don't know how he got it, I tested his water and it was 0 ammonia. Maybe my test kit is broken, but I change the water regularly anyway, so I don't see how it could happen. Could anything else cause finrot?
Also, I was considering treating it with aquarium salt, but the problem is his raise scales are actually an injury. I think he just have got danged against an ornament at some point. :/ I am pretty sure salt would really hurt him if he has no scales on a patch of his head. How do I treat the fin rot?