Green Montipora cap turning brown

[GuppyHJD]

I started with small frag pieces of red and green montipora cap which have been growing in several parts of the tank. They have been growing for almost two years. Now, the green montipora is not looking good. the center of the colony is turning dark/brown. What could be the problem?

 

[KrisReef]

Kinda looks like it might be importing symbiotic algae from another coral? Commonly called “grafting” but the term is not technically correct.

 

[GuppyHJD]

Kinda looks like it might be importing symbiotic algae from another coral? Commonly called “grafting” but the term is not technically correct.

So my reds and greens are going to turn brown?

 

[GuppyHJD]

Suggestions on how to get them back to their normal colors?
The red montipora seems to be losing polyps?

 

[gbroadbridge]

I started with small frag pieces of red and green montipora cap which have been growing in several parts of the tank. They have been growing for almost two years. Now, the green montipora is not looking good. the center of the colony is turning dark/brown. What could be the problem?

I don't know your Water change schedule, but have you checked Potassium levels?
My monti's have a quite high K demand and I need to supplement

 

[GuppyHJD]

I don't know your Water change schedule, but have you checked Potassium levels?
My monti's have a quite high K demand and I need to supplement

My potassium is 498, which is elevated from the recommended target of 420.

 

[taricha]

Your other monti caps on the right in the picture are low color / pale also to my eye.
Are other corals happy at current parameters?
If you are doing low/no water changes, I would consider change to a more standard 10% per week if it were me.

 

[GuppyHJD]

Your other monti caps on the right in the picture are low color / pale also to my eye.
Are other corals happy at current parameters?
If you are doing low/no water changes, I would consider change to a more standard 10% per week if it were me.

My hammer is not growing. The birdsnest, slimer and digitatas are happy. Duncans are so-so. Torch seems happy. The 3 week addition - plate coral is not looking happy. Yes the red monti is turning pale too.
I am doing 25% water change each month.