Sps bleaching out?

[Reef Mechanic]

I recently decided to switch salts from aqua vitros salinity to red seas coral pro salt mix. Red Sea has higher levels of Ca,KH, and Mg. which is supposed to accel growth. Being that I was looking to accel growth on alot of frags I thought it was a good move. I was wrong I think I might have changed to much to fast. I started water changes 3 days ago changing 5 gallons a day. Except yesterday I did 10 gallons. About 2 hours later many of my sps started retracting the polyps and fading. This morning almost every coral has lost significant color and retracted polyps. Not sure if I brought levels up to fast with water changes or what? Any suggestions would help.

Tank 92g corner with 29 gallon sump
Before water changes.

Ph-7.8
Alk- 7.7
Ca-370
Mg-1280
PO4-0
Nitrate-0

After water change
Ph-7.4
Alk-9.3
Ca-420
Mg-1380
PO4-0
Nitrate-0

 

[Schism]

I recently decided to switch salts from aqua vitros salinity to red seas coral pro salt mix. Red Sea has higher levels of Ca,KH, and Mg. which is supposed to accel growth. Being that I was looking to accel growth on alot of frags I thought it was a good move. I was wrong I think I might have changed to much to fast. I started water changes 3 days ago changing 5 gallons a day. Except yesterday I did 10 gallons. About 2 hours later many of my sps started retracting the polyps and fading. This morning almost every coral has lost significant color and retracted polyps. Not sure if I brought levels up to fast with water changes or what? Any suggestions would help.

Tank 92g corner with 29 gallon sump
Before water changes.

Ph-7.8
Alk- 7.7
Ca-370
Mg-1280
PO4-0
Nitrate-0

After water change
Ph-7.4
Alk-9.3
Ca-420
Mg-1380
PO4-0
Nitrate-0

I think your ph is the problem. A jump like that can really irritate sps. I would double check your salinity as well. 7.4 ph is not going to be sufficient for coral growth. 7.8 is about as low as you wanna see.