Update [8pm local time]: my hospital tank wasn’t quite ready, but I had to dump the sick seahorse in it a little early. She spent the evening resting horizontal on the sand bed. A few minutes ago I saw her on the sand next to a coral. I watched a bristleworm venture out, and eventually grab on to her snout. She fought it off and jerked around, but for awhile she was up in the open water with a long red bristleworm stuck to her snout. After it dropped off, she fell back to the sand again.
I immediately grabbed her and tossed her in the hospital tank, with no acclimation.
Main tank is 79 degrees, 1.024 salinity. Hospital tank is 72 degrees, roughly 21 or 1.016 salinity.
But she’s in there now. Still, no medicine, and no food.
I’d have to guess that it’s unlikely she’ll be alive in the morning. Very sad.