Ohh that is what Synthisis (my bf) keeps dealing with. Neptune's tail will begin to heal, and then you turn around a few hours later and it is back to where he began. It's like it is a never ending process.
It sounds more to me like he enjoys a lack of activity vs. a lot of activity. I'd put him somewhere with less activity or noise and just do weekly maintenence. If you can't move him somewhere quiet, you could cover him up. Don't change his tank around anymore. Just think of him as a library. Try and keep things quick and quiet. Do you play loud music or a TV? Maybe it's quiet he likes vs. a certain setup.
I never play loud music and keep my tv VERY low (I have roommates I don't want to disturb).
Since I think I'm going to put him in the 2.5 he will be able to see my whole room so I might have to cover his tank up. I'm worried though because I'm going to cycle the tank and that involves a lot of water changes so for a few weeks he'll be getting a lot of activity. But he has been through a cycle before and wasn't worse for wear so I guess he'll be ok.
I wanted to get ghost shrimp and put in there but I think I'll just let him have that tank all to himself.