Nitrate @5-7.5ppm with hannachecker. 1.025salinity around 8.5 alk (hanna) yes they was 0-0 around 3 mounths ago -> cyano -> all that taken care offSince it’s affecting multiple types of coral, guessing not a predator. Probably toxin or chemistry, if it were me I’d be doing a ton of water changes and running carbon, striving for 100% turnover in a week. Curious if your nitrate and phosphate is bottomed out.