Obviously I don't want to sound pushy, but this guy couldn't take up too much space. The care you would give him would trump any sort of care that he is getting in that tank. I'm willing to bet he's probably riddled with mites too. Itchy as hell & bitten all over. Gosh, I wish I could go get him
If taking him in is absolutely out of the question then definitely call the ASPCA. He deserves so much better than to wither away.