I have 4 if them for my 300 gallon thinking the return pump pumps 2,800 gallons and the filters do 600 gallons each. With all the elbows you lose flow so actually 2 would have been enough. I like them alot. I know what I did was drill 4-1 ¹/² holes in the lid on one to let it breath and the filter doesn't get so water logged, I will be doing that on the rest. I didn't have any odor