Originally Posted by Bandit1200
In my opinion and experience, the polishing pads are the weakest link here. It doesn't take all that much to crud them up to the point of completely clogging your filter. You'd be amazed at the stuff that will clog them up that you can't even see in the water column.
One experiment would be to start servicing the filter monthly and replacing those pads to see if the flow keeps up.