I started with a pair of adult m/f albino oscars in my 450 gallon with a 120 gallon sump. I introduced a new adult pair in the same tank. The old pair split up and the male went with the new female. My problem is the female that got the boot has the signs of hole in the head. Since I haven't had this problem in my other tanks with cichlids I was wondering if it could be from the sump? I have heard that things like canisters and sumps breed the type of protozoans that cause hole in the head. I was also thinking it could have also been caused by stress of the pair splitting up and the male harassing his old partner. I do regular water changes every week and tank maintenance shouldn't be a factor. So what gives could it be stress or the sump or a combination of both?