i tried 10 gallons... during the summer you will have intense evaporation and your salinity level will drop drastically unless you refill it with new r/o water. if you have the time, it's fine, but, try to go with 30 gallons as TripleT said, but if you must go the lowest, i would say 20 gallon. I had a 20 gallon long a while back, it was easier than the 10 gallon, but now i have 40 breeder cuz i didn't want to hassle with it. you literally have to be on your toes... also, there aren't that many fish that can live in a 10 gallon unless you like to watch gobies.