I've had a 55g tank with 9 goldfish (using an xp3 rena filter rated for a 175 g tank) since 2000. I also have a pleco, 2 dojo loaches, and 2 corydoras cats in the tank with them. About 4 days ago, I noticed that one of my goldfish were missing both eyes, otherwise the fish was acting healthy. Then this morning my nice big black telescopic eye black moor is missing his eyes. He had them yesterday. What's going on here???