Marbled/Snowflake Moray, anyone own one or have any exeperience?

What's the salinity? These really are not true brackish animals but rather the juveniles that inhabit estuaries and river mouths, then migrate to the ocean as adults. Could be the low salinity is making it unhappy. I've had success with crab and lobster legs enticing eels into eating, so you may want to give that a try as well.

I've had a few eels & puffers over the years and the one universal truth that they both share is a love for mussels. I go to the seafood section of the supermarket and get a bag of mussels and throw them in the freezer. At feeding time, get a glass of warm water and thaw a whole mussel in the water. When you're satisfied that it is well thawed, get a sharp knife and split the two halves wide apart like a butterfly. Toss that in the tank. The first time they eat it might take a little bit for them to get interested in such a new food item. Wait two days before doing it a second time. They should be much more interested then. The third time should be a frenzy.

I had a gold spotted snake eel and a snowflake moray that were so mild mannered until I put mussels in the tank. They would wreck the tank ripping the things apart. The snake eel eventually started pulling the whole mussel under the gravel and the only evidence of the subterranean feeding frenzy was the flying gravel and occasional toppled tufa rock.

Puffers were equally vigorous in their love for mussels but less destructive while eating.