It is important to distinguish between stn/rtn and bleaching. They can sometimes look similar as a bleached coral is white as is a fleshless coral skeleton. However the causes of these two issues are often different. It looks like loss of tissue on the corals in the photos you posted. There appears to be algae/diatoms visible. Algae will not grow on living coral tissue. Just want to be sure here as It is hard to be sure from photos and I don't know how long they have been in the tank like that.
I think the most important thing to do now is get control of your parameters. Some large water changes would help. Perhaps some GFO to keep the phosphate down. Get the skimmer running again. Then when things are stable introduce some hardy corals and see how they do.