Yes when they get that big and you loose them you can't send them to the big tank in the sky by flushing. Are you sure they are trying to help him or are attacking him? I just had to move one of ours into his own 29 gallon the 125 gallon was to small with the other 3 oscars and convicts starting picking on him think they were in "mood" they were digging to make nest in gravel.my thoughts are with you