Yes I thought they were called red bugs
Ah no worries. No, red bugs is a totally different parasite problem for corals. Planaria flatworms are only a big issue if get plague proportions, as they can obscure corals from recieving light. The biggest risk is what you experienced. Killing them off forces them to lyse and release their toxic insides. It can be fatal to fish and corals quickly. If using flatworm exit or levamisole, you need to have a lot of saltwater ready for a large water change and run a good load of carbon to try to absorb the excess toxins. Luckily, the meds work really quickly. Like within minutes. Id siphon out as many as I can, treat, siphon any dead flatworms arising, water change more, and then run carbon immediately.
