I've never had a store bought filter but, I've always been told to buy them 2 times the size they indicate...so if you have a 300 gallon pond you need a filter for a 600 gallon pond....I'm just not too keen on those all together things--what happens when the pump goes out--then your having to buy a whole new filter,pump and uv...I'd buy mine sepperatly......
Lawanna