Corals do great, until they don't..

[Nebsky]

I am struggling with growing corals, I have a 220 gallon tank, with a lot of rock which was in a previous tank for 5 years before being moved to this tank a year ago.
In the past I have tried growing zoas, and a few random lps, but never had the time to really stick with it. Within the past few months I have purchased several frags and have paid close attention to water parameters, all of my corals were doing great, and growing well, but suddenly I noticed 2 chalice were receding, red montipora was turning white in sections, one favia losing tissue and cyphastrea polyps all closed.
All of the zoas appear to be unaffected and are doing well.

I have made no changes to lighting or chemistry routine, I use kalkwaser in ATO and dose 2 part when needed.
I run a protien skimmer
My parameters are:
ALK 8.0
Calcium 420
Nitrate 10
Phosphate. 06
Mag 1320.

I removed all affected frags and dipped in Seachem reef dip,
Any suggestions on what I am doing that could cause this would be appreciated

 

[Mr. Mojo Rising]

When all parameters are perfect, but corals still slowly dying after months, it usually comes down to low lighting. Lighting, flow, and nutrients are the 3 things corals need to thrive. So your nutrients are covered, can you share some info on the lighting and flow?

 

[Nebsky]

Thanks,
For lighting I am using 4 viparspectra 165 blue is at 65 white at 2, my par meter reads 265 at top of rockwork and upper 90 to 100 on bottom.

For flow I am using 2 icecap fp 200 at 60% random on right side about 1/2 way up and 2 jebao EOW-22 on the upper left side, also 60% random flow.

 

[Project1004]

“I use kalkwaser in ATO and dose 2 part when needed.”

You shouldn’t need any of these until your tank is stable and have enough coral demand. Regular water change is recommended.

 

[Shirak]

I don't see much in there that could be using a ton of Alk and Ca so I'm with Project1004 on Why are you dosing?
Also looks like most are on the rack which is on the bottom? The Monti should be way up higher.. and even 265 at the top of the rocks could be a bit on the low side. So may need to turn up the light.
I would also suggest possible nutrient issue with such a low fish load. Nutrients are there but they are kinda low

Photos with white lights on too please!

 

[Nebsky]

I don't see much in there that could be using a ton of Alk and Ca so I'm with Project1004 on Why are you dosing?
Also looks like most are on the rack which is on the bottom? The Monti should be way up higher.. and even 265 at the top of the rocks could be a bit on the low side. So may need to turn up the light.
I would also suggest possible nutrient issue with such a low fish load. Nutrients are there but they are kinda low

Photos with white lights on too please!

Thanks, I initially dosed to get parameters to where they are, topping off with kalkwasser seems to keep them at that level so I continued doing so, but I can definitely discontinue to see how it goes. The red monti had been up top, I moved it down to the rack when it started turning white, about the same time the chalice began to recede.

Thanks for the help!