Well, after much confusion on my part, I think I've finally figured out what's wrong with a female betta I got over break. Today, as I was shining a light on her to check for velvet, I noticed that her eyes are opaque. After I moved the decorations in the tank, she couldn't find her way around and was running into things. She never seems to notice when the other fish are coming at her and the one time I've seen her flare, she flared in the direction she was nipped from, even though the other fish wasn't there. All things point to her being blind. So, she's coming out of the sorority and going into her own tank right now.
I know some members have had blind fish, so I was hoping for some pointers to make things easier on her. Good or bad substrates or no substrate at all? No floater plants? And food is an issue. The only time I've ever had her eat is when she was in her little betta cup and the food sank to the ground; she found it by swimming around with her belly on the bottom. So, any ideas?