OK! I'm at the end of my rope with DD's fish. She's had them for 2 years - new bigger tank this christmas. All hunkydory until we went away in the summer - came back to 2 dead fantails and 1 ailing. Put it down to 1. too much food given by teenage minder, 2. fin rot. Treated fin rot with stuff. Third fish died. Went to ask for advice at local aquarium shop. Suggested it sounded like ammonia burn. Was told that I was cleaning the tank too thoroughly and had basically removed all the good bacteria. He sold me something to neutralise ammonia and add bacteria. Treated for a week. Took some water in to test - still too high in ammonia. Left it 2 more weeks and ammonia levels were perfect. Bought 2 more fish. One dead within 24 hours. The other dead within 48 .
Both fish has been stripped of scales (as were the original three) but I don;t know whether that happened after they were dead. One of them had quite big lumps taken out of it. DD reckons the sucking loach we bought just before the holiday is killing them. Sounds a bit unlikely but as I'm running out of ideas I'm ready to consider it. Is it possible?
The tiny pearl danio is fine. Strangely.