might find this link interesting
http://suffolktradingstandards.word...uper-aquatic-hw304b-external-aquarium-filter/
sun sun filter, not a big fan but has some great reviews. your problem may be blow past, or water is circulating to fast. they have no valve to slow it down so may want to add one, ideally you are looking for a 5x per hour on a canister and 10x on a HOB. I would add a AC 110, great reliable filter with plenty of media room, can get on sale for 60 or so, regular around 80. how do you clean your filters?
I don't think his issue is due to too fast a circulation due to the filters. Those HW304bs are rated at 525gph, which means thats the flow you get with no media at all inside the filter. With the canisters filled with mech and bio media materials the flow rate will be considerably lower.

