The thing you guys are forgetting is the reproductive stage of red bugs, from what I can remember, are freee floating larva. No way to get rid of those by just keeping an eye on a corral in the this whole tank
You NEED to remove the coral for 6 weeks or treat the whole tank with Interceptor
I think a few things need to be kept in mind.
1. There were several acros in the tank, now there is only one. Is the remaining acro one that was infected? Red bugs will not attack all Acros.
2. The individual does not have a quarantine tank, and presumably did not want to throw his last Acro in the trash. One of these would need to be done to ensure 100% the red bugs were removed. If using a quarantine, the treatment would need to continue there. Of course you can dose the DT, but I had the sense this was not a consideration.
3. Nobody knows at this point in time if there are any remaining red bugs in the tank, so in fact, leaving the coral in the tank and observing may be sufficient. If it proves to be insufficient, the aquarist can take the next step.
4. The red bug life cycle has been under much debate. I have read they lay eggs and I have read they produce live birth. I have also read that leaving a tank fallow for 3 days is sufficient, while others suggest you leave it fallow for months.
Given the circumstances for this aquarist, I believe it is reasonable to take the wait and see approach, and then make adjustments if required.
Needless to say, no additional Acros should be added for a while.