The first thing I would do is to stop feeding him in a separate tank. It sounds like it really stresses him out. Even though it seems like he's eating a lot, I have no doubt that the stress is affecting his appetite. That in turn will make him even more cranky and will also slow his growth rate from lack of eating enough.
He is very small for 4 1/2 months old. I know it seems like you're helping him out but he really needs to be left alone for feeding time until he's more comfortable. Once he gains a couple more inches, I bet he'll seem like a different dragon.