I have kept a
snowflake eel from 10" to it's current size of a little less than 30". And another from 8" to its current size of a little less than 24". They normally grow up to 30" in the wild.
Tank size for first is 60 gallons. The second is in the sump refugium. Around 10 gallons (refugium size).
Do they eat fish? Yup. But understand marine fishes know how to handle even a large 30" snowflake eel. They keep slapping Faith (the eel) on the face and tis signals Faith not to eat them. Now try putting a feeder carp (the eel enjoys that one). Once a roach dropped into the tank and .... yup...yuckkk....Faith ate that one too.
Snowflakes eat fresh squid, shrimp, abalone and crabs.
BTW none of my tank has a TOP cover. The eels are lazy fishes and mine never jumped out. And the only time an eel jumped out was when I was new to keeping them I made a noobie mistake of placing two inside a tank.
They are also very tolerant of water condition but don't take the extreme. Do aerate your tank (strong power heads and water turn over). LOTS of live rock, even
base rock for cover. The eel decides how the tank will look. LOL!
Keep them happy with a live fish once in a while.