Hi all. My 46 gal. bowfront has been going along fairly smoothly for a month or two now. Tanks been cycled, water quality good, 20% water changes weekly, no sign of disease or parasites.

Inhabitants: 6 rosy barbs, 3 black lyretail mollies, 3 clown loaches, all ~1.5 - 2.5"

A couple days ago I noticed one of the loaches was in really rough shape. His swimming seems laboured compared to the other loaches, and he often just rests on the bottom of the tank (when he's not hiding in the cave all 3 loaches have claimed as their own). I can see some kind of white-ish discoloration inside him, that runs from his head almost down to his tail. It is only visible under his orange coloration, not the black, so it's not external. As I said, no sign of parasites, though he does sometimes scrape his body against the driftwood and substrate.

At any rate, he's still hanging in there, although I almost euthenized him a couple nights ago (he perked up after 15 minutes or so - I thought he was done for). But today I found one of the female mollies pressed up against the filter intake, clearly dead. No sign of physical damage. Some strange white blotch on its face, on the intake side (not sure if this could have been due to the water flow into the filter, or if it was there before it died). I hadn't noticed any strange behavior from the mollies, and the other two seem fine.

Any suggestions on what might be going on?

The only other thing that might be relevant is that I lost a rainbow shark in this tank about 3 weeks ago. He'd been getting more and more reclusive for days, and then when I realized I hadn't seen him for a couple days I went searching through the tank ornaments. I turned up about 25% of his torso in the loach cave, and what was left of him had turned totally white.