We have recently (3 weeks ago) purchased an albino oscar and black tiger oscar.They are approx 4-5 inches long. Over the last 6 days our once dominant albino now has stopped eating and is less active.We cant see any physical problem except he is holding his mouth open slightly.constantly.We have checked PH and nitrate etc and all is ok,what could possibly be wrong with him as we are new to oscar owning.He has nothing stuck in mouth.,We have tried pellets,beef heart and earth worms and still he is uninterested.We vacuum and replace part water every 5-7 days,but have been told this might be to often,we would love your opinions.We are in Australia,so have treated water as needed.