I just want to mention make sure you have a secure cover if you do a get a snowflake. Buddy of mine lost one of his 10+ year old snowflakes due to it going carpet surfing not long ago. On another note, he did keep a lionfish with his snowflake, but it was also a 125 gal. As long as the eel is big enough to not be eaten, they're ok together. Snowflakes do get large and can become pretty aggressive... a 55 might be small side if you want lionfish as well, especially if you want anything bigger than dwarf lions.