I'm not knocking your filter, but all too often the juwel filter are not powerful enough to suck in the debris and if that is your only means of filtration in your overloaded tank, may I suggest you add an additional filter, you'll find the benefits outweigh the cost.
I have a juwel tank(their largest) and I need to supplement the filtration with 2 external canister filters, and I don't have such an overstocked tank. It's just that my fish are messy eaters!