Red Cyano(also know as red slime) ! !! VERY BAD! lol it can take over your whole tank. It's a type of algae that fish will not eat. It will cover corals and kill them, and it can spread rapidly from day to day. On my experience it's caused from a problem with water chemistry. Not using RODI water can cause it as well as bad pH or kh (not sure about calcium. In the past if I have seen it I just test the water and fix the parameters along with a water change and it dies off. It it begins a full take over it is not easy to get rid of.
Ok thank you. My zoanthids closed up and is now back open. My salinity was high and phone was a little high. Did a 10% change out and now they are open but this showed up. Now that I know what it is I can get ride of it. Currently don't test for calcium. What's the best test kit for that?
Calcium is important for corals and inverts and coraline! As far as the best it depends on how much money you want to spend, but if you haven't tested it its probably low, you might not have adverse effects if you only have soft corals