Wooa Wooa Woooa. Lets slow down here.. Vermetid snails passing pathogens. There is a TON of things that should be ruled out first before we go looking for the most complex and unique reason for problems with an sps tank.
99% of the time w/reef tanks the simplest answers is the solution.
When something like this happens you need to go down a check list.
1) How long as my tank been setup? Was it ready for acros?
2) How long have these corals been in my tank?
3) Have I added anything recently?
4) Do I have some sort of Pest? AEFW, Red Bugs?
5) What other changes have I noticed in the tank? (increased algae, decreased algae, change in algae type, dying fish?)
5) Did I change anything recently? Salt boxes, brands, media, new bulbs?
6) If you have been doing water changes, have things been getting better or worse? If worse test batch of new saltwater.
7) Is my RO/DI working correct low TDS?
8) Are all my parameters are the proper levels?
9) Have my parameters been swinging or at all (even if they are at the proper levels now?)
10) Are all my test kits current and correctly calibrated (I don't know how many times, I've replaced a test kit with a new one and had different results when testing back to back. Refractos need re-calibration, and those swing arms are often junk)
11) Has my routine changed recently? More water changes, less water changes? More time with hands in the tank (Maybe moved a frag that fell over after doing an oil change without thinking, or with soap on your hands?)
12) Is all my equipment in good working order? No cracks in my heaters, no sketchy old rio pump leaking volts, no temp probe leaking copper, or mag that I left in my tank when I should remove it after use rusting, no sponges clogged? Lights aren't old?, UV shield on bulbs isn't cracked leaking or broken?
13) Do I have kids? If so.. can they have tossed anything in the tank?
14) Have any elements around my house changed? Fumigation, painting, recent power failures, increased c02 due to closing up your house for the winter, etc.
That's all I can think of off the top of my head, there are so many other little things that are easy to overlook or forget to check. I notice you don't have your salinity listed as a parmater, you'd be surprised at how quickly things can die if that gets out of sorts. We often take it for granted to, but refractometers are easily uncalibrated, and swing arms are often inaccurate.
The last thing I would do is rip apart your tank and start over, adding stress to a stressed out system his how we loose entire tanks. Start out simple, don't over react, and when it doubt do a water change.
