Hello Pete --

I realize this thread is a few months old, but I haven't visited the forum in about that long. My pool is only 10,000 sq. ft, but I have the same pump, filter, and in-floor system as you; and, I have the very same dirt problem too, except that the it covers the entire floor of the pool rather than just a small area.

The research I've done suggests that the in-floor cleaning systems are excellent when first installed, and gradually deteriorate to being pretty much worthless when 6-7 years old. I can vouch for the latter.

If you are still around, I'd be curious to know whether you ever determined the source of the problem, and how you decided to proceed.

Thanks!

Scott