They actually recommend going with ?separate units.... in your example if you are trying to scrub 4 cubes a day 2 units that scrub 2 cubes a day would be better then 1 unit that will do 4 cubes. When you clean one unit it takes a week or 2 to really get going again. During this time you are not growing that mutch ?algae and not removing as mutch nutrients..... if you have 2 units you can stager the cleaning so it balances out everything out better. Not trying to push you into a sell but just thought you might want to take that into consideration. The guy at ?Santa Monica is great and has help me a lot if you feel like it email him to varify what I have told you.?