Trachyphyllia radiata help

[Crabs McJones]

Posting this for my uncle. He bought this trachy from liveaquaria. It's a rainbow. This is his second one. First one did something similar but much faster and liveaquaria replaced it for him. He got it, dipped and acclimated it, and after a couple weeks it starts dying off. He dipped it again and saw this in its mouth. Any thoughts or suggestions I can pass along?
His parameters are as follows
Salinity: 1.025
Ammonia:0
Nitrite:0
Nitrate: >5
Phos: .02
Calc:440
Alk: 8.6
Mag: 1460
Tank has been up and running for well over 8 years.
He has alot of other SPS and LPS in the tank and everything is alive, colorful and thriving. But he cannot seem to win with these Trachy's.

Thoughts?

 

[DSC reef]

I see tissue recession, what was it dipped in? The mouth looks to be expelling zooxanthellae or waste. Trachyphyllia are very sensitive to dips and acclimation. Typically I just give them a good once over, temp acclimate and if salinity matches or is close I put them in the tank so they can acclimate to the tank.

 

[Crabs McJones]

I see tissue recession, what was it dipped in? The mouth looks to be expelling zooxanthellae or waste. Trachyphyllia are very sensitive to dips and acclimation. Typically I just give them a good once over, temp acclimate and if salinity matches or is close I put them in the tank so they can acclimate to the tank.

He did say that he tried feeding it a little before snapping these pictures, so perhaps it's just poo.
He used coral rx for 5 minutes per the instructions on the bottle.

 

[DSC reef]

If he wants to dip future trachys then suggest seachem reef dip. Coral rx is very harsh IME. Keep an eye on that recession.