I've had my betta since the beginning of April and have noticed a white area on the edge of his body on both sides. I think he's always had it but it's bigger now. Any ideas what it might be? His fins are looking a bit more ragged at the ends which sounds like fin/body rot to me although the edges of his fins aren't dark.

I've given him one course of Myxazin which treats fin rot and bacterial infections but it hasn't done anything so far. I'm doing a water change, then should I try another course of myxazin?

Hes currently in a 24l tank whilst I do up his main 28l tank. Temperature is 25C. I haven't checked the parameters in a while but the tank gets weekly water changes of around 20%. I haven't added anything different except some stress coat before I started on the myxazin.

pictures. Can't seem to rearrange image order on mobile. Also not the best light as it washes him out a bit.