[mps9506]

A 55 will be ok for a Zebra Moray, I would suggest something a bit larger to increase the amount of water in the system to keep things nice and diluted. These guys are messy eaters. 90 gallon sounds ideal to me.
Things to keep in mind when keeping these guys:
They are great at knocking rocks over, so make sure you have solid rock work.
The ones I've had come through love hiding in PVC pipes, but if you make a network of pipes it gets really messy inside and they are kind of a pain to clean.
If you get a smaller one it will be easier to keep themin a smaller tank and move up to a larger tank as they get bigger. The smaller tanks are easier to keep secure and target feed to get them onto prepared food and off live foods.
Lastly a large moray eel has to be one of the most difficult specimens to move from tank to tank. Don't bother with a net or trying to use your hands. Get a large bag, put the entire bag in the tank and push the eel into the bag, close off the bag while underwater and pull the entire thing out. Drain some of the water out while holding the top mostly closed and and air and it's ready for transport or ready to get moved to the larger tank.