Bio Balls are engineered specifically to stop clogging.
How they work:
The reason is simple: the gaps of space within a bio ball are large and anything that can clog it up would already have been filtered by the pre-filter (such as filter wool, sponge etc). This is the reason why water filtration should always pass through mechanical filtration (pre-filter) before biological filtration.
In this way - the Bio Balls will function efficiently giving you a seamless, trouble free pond filtration system. The gaps of space within a bio ball allows for a larger surface area for the habitat of the micro organicism's that create a food chain in the bio filtration process. The different organisms feed off each other at the various stages of the bio filtration process helping create a good eco system similar to that created naturally in rivers.