Your 5.5 gallon is only big enough for two otos or one ( two if minute)
SAE. Remenber even once cycled it's still a "new" tank.
A quarantine tank needs to be big enough for the largest fish you may have
in the main tank.
I would suggest a 10g minimum and 15g would be better for quarantine.

Your tank will cycle more efficiently if you can get some used filter media
from a healthy tank.

Sue