I don't know what kind of corals you are keeping or type of system you're running, but I like to have my reef tanks turn over at least 7 to 8 times the volume of the tank...this would be at least 400 gph minimum. A canister filter wouldn't do this efficiently. Are you using an overflow box...
I didn't think just one would work on a tank as big as 55gallon. I was thinking about putting them in series. They interest me because they seem to be pretty quiet and efficient? I guess I'll have try it out for myself.
Has anyone used these small Thermocline Chillers? I was wondering how effective they are on 20 gallon tanks or larger...also how well do they work when they are piggy-backed?