Adding a cleaner shrimp?

[Lavabrine ninja]

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.

 

[blaxsun]

There's typically a reason for before... (guessing the shrimp may make a nice, light snack).

 

[exnisstech]

I had a 30+ inch zebra moray added after my skunk cleaner shrimp x2 and my shrimp would clean the eel. Everything was fine for about 6 month then my picaso trigger started nipping the eel and it went off food.
Edit : this was a 180g with lots of rock