I have 2 Oscars that have been in a tank together since they were babies. Although they were both the same size when I got them one has grown much bigger than the other.
Recently the biggest one has lost all his colour, isn't eating, and sits at the bottom of the tank seemingly gasping. Everything in the tank is registering as OK..........we have checked ammonia levels, ph etc. everything is reading perfectly. We are doing partial water changes regularly, filter cleaned regularly, we have used an anti fungal in the water just in case that was the cause.....nothing has worked. Now the smaller Oscar is bullying the bigger one and he has quite a few places where he is bleeding. We are going to get another tank and try separating them, but could you give us an idea on what we should do to try to fix the problem of the sick Oscar?