algae problem? or somthing else

[Octoman4]

70 gallon

p04:024
no3:4+/-
ca:452
alk 8
ph 8.3
mg?
5 fish, lots of coral, lps/sps, nothing new and every thing new is dipped.
I run carbon and a filter sock its about week old and i also have a small fuge in my sump... basically for the last 2 weeks my coraline algae has been dying off fast... all my coral are doing great though. i noticed today there is a "slime" layer over alot of the rock. its only the rock that is getting light also. all the rock that isnt getting direct light is still super purple
i got the red sea no3 p04 x to try to help ... any ideas on what this is?

 

[Octoman4]

Bump any one seen anything like this?

 

[gonumber24]

When mg drops, coralline disappears. Check your mg level. Should be around 1250 to 1350.

 

[Octoman4]

Ok cool thanks

 

[Octoman4]

Bump, I use ro water, and the lamps are 4 months old...