Yes def. need a lid on top and as long as there are no openings at all. I had 2 eels, a Black ribbon eel and a snowflake ee. I loved my ribbon so much because I had finally gotten it to eat after a month. There was a tiny hole near my protein skimmer and 1 day, they were both just gone. Til this day i cant find ny snowflake but I did find my ribbon after a few months :/.
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