Help,not sure what this is on bottom of pool

[matt4x4]

That's the same stuff I fight every onset of fall, this stuff needs tons of shock 20-25ppm, AND DE in the sand filter to heplp grab it, if you flock once it's dead, it's relatively simple to vac up manually, however, the auto vacs seem to blow it around more than anything, BTW - the stuff in the pic is the live stuff, once you've killed it you'll get that light blue foggy water look - vac it up VERY slowly once dead (manually), you'll backwash at least twice over the course of cleaning the pool, this stuff is nasty and likes to stick around - even at 15 ppm.
Keep it at 25 ppm for 24 hrs, you'll kill it and won't have to replace your filter!

IT IS NOT DEBRIS, matter of fact, vac it up with DE, backwash and you'll see how green it looks, leave it in the pool, COVER if you want, it multiplies - dirt doesn't multiply....