Is this algae? Or problem with DE filter?

I know this is a bad picture (cell phone pic), but this is what keeps appearing on the bottom of my pool:
http://i78.photobucket.com/albums/j1...oldeposits.jpg

When running the filter, the water coming out is strong and clear. My pool is crystal clear. It's just this "stuff" keeps settling on the bottom. It vacuums up fine but then the next day it's back. We have styrofoam underneath our liner and it seems like the "stuff" settles in all the cracks. It's like a dusty stuff. It's not "attached". We have a Star DE-50 filter. Also wanted to mention that when I turn off the filter to empty the basket and then turn it back on, it start shooting out a slighty rusty colored water and then quickly turns to clear. I keep taking apart the DE filter and squirting off the grids and recoating it, but I shouldn't have to be doing that as often as I am. When I take it apart, the grids are covered in a lime green "gunk" with no evidence of DE so I'm thinking somehow the DE is possibly shooting into the pool? We are having a pool party Sunday with 21 people and some are kids. I'm hoping I can vacuum right before they come and the pool will be fine to swim in as long as this "stuff" isn't dangerous. Any thoughts? Thanks!

Should probably post a complete set of current water testing results. In my pool, I continually have dust that settles in straight lines along the bottom of the pool. The guy who installed my liner laid a pink foam under it and duct taped the pieces of foam together. This is just enough of a depression for the lines of dust to gather. When we get in the pool, it gets stirred up and then settles back down. Maybe you are having the same type of thing going on in your pool.

My thoughts exactly Mom.

Denanbob, are there actual physical depressions where this "gunk' is collecting? They don't have to be very obvious or pronounced just slightly varied.

You've got something going on with the green build up, which might be some how making it back into the pool. I'm not a chemical guy, I'm more of a nuts and bolts one, so I can't help you on what the DE is extracting from the pool. But, have you checked for a small tear in the DE grids, or some of the stitching letting loose? Is your mulitport, or whatever valve you use seated properly after you back wash? It could be sucking residue from you backwash line. Is the back wash line clear and free and not "backing up"?

Added: Have you rinsed the bottom of your DE filter body, out the winterizing drain?

For the short term it appears the volume of "gunk" is so small that a quick vacuum of the pool before company would suffice. Even a quick brushing should cause it to suspend for a while. If there's any activity in the pool in that area I doubt you'll see it most of the day. Hope for sun and hot day, with 21 people I doubt it will have a chance to settle. ;-)

Watermom...I'm hoping that is what's going on (dust settling). I will have to post test results later but everything looks good in that department except my alkalinity and calcium are high. It's a vinyl pool so I didn't think calcium mattered and I've fought my alkalinity for 3 years to no avail. CANNOT get it below 160 no matter how hard I try. However, I'm not having any trouble with my PH (varies between 7.0 on super low side up to 7.6 usually holding steady around 7.4ish). And yes, my liner has little folds like you where you can tell where the foam underneath is duct taped and that is where the "stuff" is. It is all along there in a perfect straight line.

VinylGuy.......my filter doesn't backwash. It just "bumps and swishes". I will carefully check the grids to check for tears, hadn't thought of that. I also don't know if we have a "multiport valve". We have a connection with a handle that we turn on or off to allow water to flow into the filter. Is that the same thing?

The pool party went great with no evidence of "stuff" settling. The pool is crystal clear. This morning, I went out there to turn the filter on and add chlorine and there was still a little bit of white stuff but not a ton. It seems to be mostly in one spot (across where the return jet pumps the water out so that's why I was wondering if it was a filter problem).

Thanks for the help both of you! I appreciate it!