PLEASE HELP WITH CHALICE

[Hunter1036]

So I️ woke up this morning to a big white spot on my chalice. What would be causing this and how can I️ fix I️t?

 

[Hunter1036]

It’s on the bottom right of the chalice

 

[DSC reef]

Hard to tell but looks like a patch of die off. Check for parameter swings like alkalinity. Anything close by that has sweeper tentacles?