Brain coral dying

How would an overflow box on the side cover your display? I had to put mine on the side and you don't notice it too much.

The tank is square and it's backed into a corner. Placing the overflow on either of the exposed sides would cover a large part of the display. There is only about 2" of spacing around the back of the tank.
Sorry, I shoulda just put up a picture at the beginning to make it clearer.

Do you guys think I could fit an external overflow into that small of a space? I bought some acrylic tonight from Lowes, but it was super thin stuff. It's gonna be a small project so if nothing else it can serve as a mock up.
I'm not seeing a lot of improvement. On the ridges that stick out a little more, the undersides are getting more color and are thicker, but overall the coral is still looking pretty terrible.

I have yet to order anymore test kits. I do know they are off though, tested a fresh batch of water and had way off results. Plus everyone of my other corals is doing amazing.

I put the coral under an overhang so a small portion of it is getting light, and the majority is getting indirect lighting. Is that OK?

I think that's okay. Sorry you couldn't determine what exactly was wrong. :( It's always frustrating when one thing is doing poorly and everything else is fine.
When I burned my brain under too much MH light, it took a long long time for him to come back but he did eventually heal.