Hi I’ve had this fish for about 3 months and unlike this brothers and sisters he is the runt who never grew. Just now I found him behind one of the decor with a massive white thing on his side. He quickly went up to the surface and did a couple flips so I quickly set him up in a 10 gallon quarantine. If anyone can tell me what this is and what I can do I would appreciate it. Ammonia is 0 as well as nitrite but nitrate was 5.0. PH is 7.4-7.5 and temp is 76 F. Thank you.