My Otto has cotton wool like fungus on his head which has just apeared today. I am going to move him to a smaller tank to treat him but I am unable to as I am out of the stuff i use to treat tap water with and there is not enough water in the smaller tank. I am going to go and get some tomorrow but do you think it will be alright to keep him in the tank he is in now or will it spread and infect my other fish? also how hard is it to treat?