Was it biopellet?

[Myka]

Originally Posted by mrhasan

Here's a video for you to judge the flow

Hmm, looks like more than 1600 gph to me. It does look like it is doing quite a good job of creating flow throughout the tank since you have your rocks designed to work with the single powerhead well. Good planning.

My "official" guess then is Xenia Syndrome (my own term lol). Sometimes Xenia melts for no apparent reason, other than the tank has aged. It seems like Xenia prefers new tanks, although this is not always true. The rest of your corals should be ok with a couple waterchanges and some fresh carbon.