Thank you! I'll do that.From what I can see, @Essjay is right. Although there isn't anything which can reverse it, the fish can still live happily. Pick a corner to feed the fish from incase he goes completely blind so that he can find food easily. You can tap the rim of the tank at feeding times so that he knows there is food. I'd up the volume of water you change, weekly, to 50-75% also