After losing or nearly losing several "smooth skinned" Acropora in CoralRx, I quit taking the chance. Those are the only corals I've ever had a problem with using CoralRx on. So, I just use Lugol's. The best I can generically say is "smooth-skinned acros". If I was to give a list, it'd consist of A. echinata, A. caroliniana, whatever sp the ORA Aussie Delicate is, A. paniculata, and A. turaki. Those are just the ones I've had personal experience...but I would extend my personal experience to other smooth-skinned Acropora as well (better safe than sorry!)