Hi:
Snowflake eels......
I would do a search here as this topic has been covered before.
They get about 25-30" in length, stay fairly thin. They are muscular enuf to dislodge rockwork and such, and they spend the majority of their time hiding in the rocks, expect to take it about 1 to 2.5yrs to reach full size.
When they are young they will eat thawed shrimp, fish flesh, crab chunks, and as they mature they will also start to potshot tankmates.
As you know eels are almost totally blind and hunt by scent alone. So they get excited when foods is in the water and strt snapping at anything passing in the scent trail.
Small fish are the most in danger, but in general terms snowflakes are fine.
If you have a 30now i would expect you to have to upgrade w/in the next yr.
As far as a green moray eels......NO..this fish will eat all of its tankmates, your clown might last 2 to 3 days. Also remember that green morays get about 4-5ft long and in excess of 100lbs. Not really a good fish for the home aquarium. An LFS has a 4 footer in their 40,000gal display tank.