Okay stop freaking out. We can do this

. Hydrogen peroxide dips and anti-pest dips are your friend. Maybe even freshwater dips if you think the situation is bad enough. The trick is to dip often enough to kill the adult spiders and the baby spiders before they get to reproduction stage.
Definitely get the infested frags out of your tank ASAP, they will crawl off the AquaSD frag and onto any other zoas you have. I would put them in a separate tank entirely or a bucket with an air stone and frequent water changes to avoid contaminating anything. Dip dip dip, inspect, scrub, dip again, keep repeating for at least a month, 6 weeks to be super extra safe. Toothbrushes, spoolies (disposable eyebrow brushes), razors, hydrogen peroxide, anti-pest dips, iodine dip, and perseverance are extremely important. Of course, you could always choose to cut your losses entirely and chuck the frag; or you can cut 1-2 polyps off the infested frag and treat them intensely, throwing away the main colony.