Hi HeatherC,
I hope the images in these threads display OK. You can see how small pollen particles are compared to sand. If you disturbe the water around the stuff with the vacuum or something like that and you see a cloud form, chances are it it pollen or it could be fine silt from the water supply. If you can get a sample and look at it closely the grittiness of sand will make it obvious. If the stuff is at the shallow end you can use a basting syringe to suck up a sample. Squirt into a cup and let it settle. Sand will settle fast, pollen or silt will take a long time. If it is fine stuff then there are tricks adding DE powder to your sand filter to trap the small stuff.
Hope this helps.
Al

http://www.poolforum.com/pf2/showthread.php?t=6799

http://www.poolforum.com/pf2/showthread.php?t=6744