Maybe they hitchhiked in on something else. Or possibly you had a wrasse or something that was keeping the numbers in check enough so the numbers stayed small. Who knows.
I remember the days when you could just put any coral in the tank and not have to worry about this stuff. Years ago I bought several sickly corals at reduced prices from some stores and brought them back to life. Now I stay away from corals that don't look right.
BTW, the corals I got from you are doing great. I did have an alk spike when I was working on my kalk reactor and accidentally let some raw kalk out in the sump and I had a few burnt tips on some of them but they have recovered and are growing.
