Leopard wrasse getting very thin

[ScubaSteve]

I might be missing something here but there is an obvious factor here: the food. You said the previous owner fed pellets but you are feeding frozen. If it ate pellets but is spitting out frozen, feed pellets. It may actively pursue the food more.

My Potters Leopard is fairly ambivalent to most frozen and live foods and will only nibble when there, if at all. But damn it loves pellets. It will out compete my anthias for pellets.

If your other fish are mostly pelagic feeders, you could try making a seafood/pellet mush and smearing it on a small rock, then freezing it. Put it in the tank the next day and the wrasse can pick off pieces as it thaws at its leisure without needing to compete with tank mates. This works well if you don't have many other fish that feed off the live rock.