Today, Indigo passed away. I'm not sure what was wrong with him. He had grown a lump/swelling where his pectoral fin met his body. I'm thinking it was a tumor. I tried epsom salt and API General Cure. Nothing worked. So, I put him back into his normal tank after treatment & kept him as comfortable as possible because that was all there was left to do. He died peacefully. I don't think he suffered. He never breathed hard or struggled to get air. Just laid on his leaf & popped his head up for air once in a while. I'm glad he does not have to be sick anymore. He will be missed.
If anyone wants to see the thread I posted about his sickness (& maybe make a guess to what was wrong), you can find it here.