Ok good

Cut off the dead parts. What's the surrounding corals within like 6"

Preiously, there was a monti pokerstar, an acro, a stylophora and the chalice (which was like 6" below) and now, in the new location, there's magician paly, a green zoa and a monti confusia (or something like that; I can't remember the exact name).

I was thinking its either because of the chalice or because of the low alk. Is it possible to have STN due to low alk?

Yep low stn I believe can be related to low alk

How low is it right now

SPS are sensitive to alk swings.

We notice STN if our alk drops bellow 6.5dkh.

Mine reached 5.4 before starting to dose haha. I have taken it up to 7.4 but every 12hours, I have noted that 1dkH drops. Ca remains 430-440 while Mg is like 1300.

Here are my current levels:

Ca: 410ppm
Mg: 1275ppm
Alk: 8.0dKh

Right after WC, my levels were:

Ca: 440ppm
Mg: 1380ppm
Alk: 7.7dKh

I am just dosing alk.

WC due on this Saturday morning. I am thinking of moving to 5 gallon WC every 3 days now :(

Definitely some kind of tissue die off. Two possibilities here that have both been mentioned. One being the sweepers of the chalice at night and the other being that its not happy for some reason.

Hope you get it figured out. Good luck.

My tank is sps and I do a WC every three days. While some as it not cost effective its 60 gallons a month which most people with bigger tanks do biweekly. I have great growth doing it this was and more nutrient export

Though I am looking at a nano ca reactor as the coral will become more demanding as it grows

What's the reasoning for this?

I do a 5 gal on tues and 10 on Fridays. Only because I don't dose or have a reactor yet

It works good to keep cal and alk up without big swings

I am buying a ca reactor soon here so that will stop when I get it