SaltFan, I no idea in what type of moray you are feeding there, but silversides and mysis shrimp? I not bother with silversides for most eels they do nothing for your eels diet and I have to guess your feeding feeders as well.
AtlFish, you need to for one thing make this tank ready to house the eel of your choice by having a load of LR and depending on the amount of LR, water currents. You as well want to not have any openings that they could escape from in which you might heard it is called carpet surfing.
And if you so young a moray, you need to block your overflow box from becoming an escape route. You will hear of some item called egg crate, I only know it is light and nothing other then that, But myself, I wouldn't suggest it but others buy it because it is so cheap. I did however hear of some who kept eels with this egg crate that their eels found a way out of their tanks.
For the eel of your choice, you need to accommodate it with a proper lair that it can conceal its whole body in darkness. Also there be any number of fish that is not advisable to keep with any eel species. Like triggers or puffers as well ding on the species of eel, groupers as well.
You will hear from others that this will work, but can those who tell you this guarantee you that nothing will happen. And also depending on if you a larger eel species, you might find that you need to weigh down the tanks cover. And another thing best to do is duct tape the top back of the tank.
You be needing for the major fish eaters, fresh strips of fish, shrimp, squid, octopus and crab* (depending on the species) as well as other ma one could use for food. Also be sure that the food you buy is from the oceans and not freshwater foods and this next thing will be of your chosen, I not buy farm raised for my eels.
As for what you can ask your lfs, that be a tough one for you need to learn first if you can trust their answers to your questions.
I have damsels with my eels and not as my main fish for as well these damsels are the same I added to these tanks almost 1.5 yrs ago. I not added any new damsels since then.