Thanks SPLACHIE. For 400 gallon, I would suggest a 4 1/2 OD tube with a footprint of 12X12X21 total height. And for the 200 gallon, it would be 12X12X15 total height. You will also need a pump to run the unit. I suggest a Mag 3 pump or similar pump to run the the unit. Also, I believe in reef...