So, just an update. We put 2 zoa frags and 1 paly frag in the tank. After a few weeks, our son started waking up at night coughing. This got worse and worse for weeks until it became an every night thing requiring a relief inhaler.
I read an article in Coral Magazine about these things and just how toxic even a few grams of it can be. Got to thinking about all the bubbles popping in the skimmer and sump and thought it would be worth seeing about to remove them for a while. Fortunately, I was able to re-home them in a friends tank.
Immediately, my son began sleeping through the night and hasn't had an issue since. That was nearly a month ago.
Suffice it to say, we won't try them again.