I use a filter pad for about a week, maybe once a month.

I put a polyfil block in my bubble trap in the sump. It takes about a week to get completely clogged. When the water starts to to back up on top of the pad I I know it's time to remove it. It also changes from bright white to brown as it clogs.

I get the poyfil blocks at Wal-Mart, in the fabric section. They are used to make pillows. Cut it to size with scissors for a tight fit. I get 4 pads from a block with some left over.

When I pull the pad out, it's inhabitated with thousands of pods.