the same is happening in Europe, i'm making the difference because now may traders are keeping corals in the country for some days and then sell the corals so it could perfectly happen that a pest could be established in the quarentine tanks (it was a theory with catalaphyllia, you remember?).
In any case, I have lost a blasto an oxypora, and echino and..... a red fungia. the question is when I've lost them and a lost all but the fungia one year ago very quickly. The fungia started to recede a little bit by then, especially the under side, so I dipped the fungia in a solution with iodine and then the recesion stopped.
Last week the recesion started again (it coincides with a drop in temperature, this winter in Madrid is very cold -7 ºC in the morning and I forgot to connect one night the heater after clenaing up the tank).
Yesterday I saw the black 1.5- 2.5 mm black critters you are describing in the thread. In my notes from a year ago a have also dicovered the same but I didn't give it importance by that time.
What I want to add to the threat is that it could happen that the bugs you decribe could be living latent in small numbers feeding on other corals waiting for the opportunity to feed on the more tasty ones when you add them to the tank.
If it is the case, once there is an deadly episode then without treatment no case to be sure that it couldn't happen again.
Sorry for my English