The seahorse died by that evening. The other horses looked great and continue to look great, so maybe it was unrelated. Still sad though When I pulled her out I looked closely and couldn't find any sign of injury or illness.
Subsea, I frequently stir the sandbed to feed my gorgonians and other filter feeders, but I don't stir under the rocks obviously, so that's why it kicked up so much detritus. I had/have my canister filter hooked up with a bunch of carbon and fine filter floss. The water clears up very quickly, so my main concern was the detritus left settling on all the coral. Yesterday I spent a lot of time trying to siphon off what I could. The tank is so deep that towards the bottom, where most of it is, I lose quite a bit of fine control and suction. As long as the corals and fish continue to look fine, I'm just going to leave things alone for a while and let things settle.
Turns out my pH meter doesn't work, so I just hooked up an airline anyway to be on the safe side.
Thanks again for the help