Dammit, all of the good guesses are taken and I really wanted that money to put towards a speed stir 
Ok my way way out of the ball park thinking just in case all the likely results come back negative
- Part of your cartridge filter ending up in the pool cos you have a super-over-humongeous sized pump
- DE that blew through the holes mentioned above
- A light coloured deck surround that you are tracking in with your feet (or your motar / grout)
- White plastic/nylon brush particles from your pool brush or robot
- Aluminium floc that you used like 6 years ago
- A jealous neighbour dumping tissue fluff into your pool just to annoy you cos you have better water than him....
Personally my money (well actually yours) is best laid on calcium scale at the moment, but I figure you gotta be in to win
Ok my way way out of the ball park thinking just in case all the likely results come back negative
- Part of your cartridge filter ending up in the pool cos you have a super-over-humongeous sized pump
- DE that blew through the holes mentioned above
- A light coloured deck surround that you are tracking in with your feet (or your motar / grout)
- White plastic/nylon brush particles from your pool brush or robot
- Aluminium floc that you used like 6 years ago
- A jealous neighbour dumping tissue fluff into your pool just to annoy you cos you have better water than him....
Personally my money (well actually yours) is best laid on calcium scale at the moment, but I figure you gotta be in to win
