Thanks all, for your suggestions.

The pool has a large, cartridge filter, if that makes any difference - oh, and I dumped the soda ash right into the pool proper. Pouring the it into the skimmer would've been a GOOD idea!

The filter's been running for 30 hours or so, now. Letting the dust settle, so to speak, sounds like a good suggestion. I'll see what it looks like tomorrow morning, and hope I can vacuum it up.