If I remember correctly you just started this tank right? How are your water parameters doing?
IMO for a 55g I would get nassarius snails, cerith snails, some astrea snails, maybe 1-2 mexican turbos, a couple of emerald crabs
BUT...Not all at once...after your initial cycle, I would add just a few snails...test water, after a few days of 0 readings, you can add a few more any then a first fish