Particles at the bottom of the pool

[barry]

I have light gray particles (but look like patches - about a 100 of them) - they are on the bottom of the pool - the water is clear except for these gray patches - I believe it is just dirt that cant get filtered. They easily brush away and then several hours come back. I tried vacumn and even backwash vacumn but they still come back. It is not algae. They have been around for 3 years. Do I need to add a flocculant or something.

[Buggsw]

What kind of filter do you have?