Yes, the "crap" on the bottom is dead algae, combined with the other normal pollen, dirt, etc that blows into the pool on a daily basis. The link that you put in the above post for the clarifier was actually a repeat link for the phosphate remover, but in any event, a lot of the clarifiers also contain a flocculant, designed to make small particles clump together and go to the bottom where they can be vacuumed out. Just keep vacuuming this stuff out as much as you can--I would vacuum it to waste and bypass the filter, that way you know it's going OUT of the pool. Just make sure that you switch your pump to "rinse" before going back to "filter" to rinse all the residual out of the pipes.

When you get ready to add the DE, like Carl suggested, start with a very small amount and wait several (up to 30) minutes before adding more, because the pressure rise can be slow. You don't want to increase your pressure more than 1 psi. If you overshoot it, just backwash it out and try again.

Janet