I want to add a cleaner shrimp to my reef aquarium. But, I have a zebra eel and have had for over a year now. I've read that to add the shrimp before the eel but can I add the shrimp after already having the eel? Right now he mainly just stays in his cave. The only time he'll come out is during feeding or if he's not been feed in awhile. He'll start go out of his cave but normally stay at the back of the aquarium. I feed him once a week and keep feeding him till he doesn't take the food.