once washed and sanitized it would work good for a sump although in my opinion a touch small for a 55g tank
I would recomend a 20g tank for a 55 sump
the rule I go by is make the sump at least 1/3 of your tank size this way you have 20g of space with 10 g of water in the sump and 10g of buffer space for when the power goes out |