My 20g aquarium

This is my 20 gallon aquarium. It started out as my primary aquarium after I had to size down from my 55g. When I upgraded to a 36g bowfront I decided to use this tank as a quarantine. I have a puffer that tries to eat anything that moves so I just decided to keep him in here. The only thing he hasn't tried to eat is my black ocellaris clown, so I keep her in there with him for company. When I get new specimens I need to quarantine, I put up a tank divider so puffer can't get to them. It has a very shallow sand substrate and two small pieces of live rock. The water quality has stayed consistently excellent and has even bounced back from coppering with no problems. Probably not the best setup for quarantining, but what the heck.