I am going to jump in on this discussion. I have an IG(38,000 gals) gunnite with the same problem. It also started after our pool company put in new sand last Spring(05) after a bad Cicada season. The pool guys admits it is sand, but says it is not from the filter because it is a different color(tan vs white). We did have a bad spider gasket and had to replace the whole top assembly on our filter this summer(not a hard job after we found the part). Our sediment may be somewhat different. It has a grit to it(sandy), but also is a little slimy. It also stains the pool if you do not get it out everyday, which sometimes just isn't possible. If I am understanding everybody correctly we should take some sand out of the filter and put it on some paper and see if the color matches the pool sand, bypass the filter in someway to see if that stops the accumulation and also check how much sand the 10 year olds from the pool company put in our filter last Spring and if necessary take some sand out of the filter if it is there is too much.

I'll get back to you.