Alkalinity

I can say without a doubt that if it is good LBTR and if you cleaned it properly with a high pressure spray, the LBTR is not the reason for the problem. Any past problems with LBTR have been found to be due to improper cleaning. LBTR is Calcium Carbonate, the same mineral that LR is made of.

If this is true LBTR and it was cleaned properly...
- First thing I would do is look at the other coral, especially SPS for signs of stress. Anything?
- Second thing I would do is check my test results with that of another kit. 20ish Alk and 620 Ca is practically impossible. It would be snowing (precipitating) in the tank before getting that high.
- Third, what is the pH of the tank?
- Fourth, what kind of salt mix? Did it change recently?
- Fifth, still thinking.
- Sixth, what is the recent history of testing results and additives?

How about a pic of the tank?

FYI, You can never believe the negative the LFS say about LBTR. They think it's bad for business so they ridicule it all the time, even our best, most supportive LFS has issue with it. 

After roughly a 10% water change yesterday.  The tests results were lower today than.  Alk still a little high at 14-15, Calc was 460 or 480.  Cant remember.  ph tested ok (cant remember the exact #) nitrates were down below 10.  I have not tested for magnesium though.  I only have the one SPS (Monti Cap) and it is only a small frag but from the looks of it about half of it is showing signs of stress.  All my other corals are doing great.  I will have the magnesium tested tomorrow when I do another battery of tests.

20,000 Mg? On what scale is that? ppm? That would be impossibly high when normal Mg is 1200-1400 ppm

A temporary Alk of 20 is not a big problem and an Alk of 14 is definitely okay and it is dropping. The Calcium and the Carbonate may be precipitating as crystals on the sand. You won't even see the evidence. A temporary Ca of 620 was no problem and it is dropping. The okay ranges are Alkalinity 8-14 dKH and Calcium 350-500ppm. The worst is when either of those are below range.
All other coral are fine.
You have a new tank, and you appear to be a new hobbyist with your first SPS frag. This is not so unusual for an SPS frag in a new hobbyist tank that is less than ~4 months old. SPS is a thin delicate skin over a scalpel sharp skeleton. It can die in a day. This is the hazard of SPS coral.

FYI, a 10% water change, depending on which salt mix is used, would drop the Alk and Ca by roughly the same 10%, from 20 to 18 dKH and from 620 to 560 ppm. So as you may deduce, the dropping values were not aided much by the water change. The tank took care of balancing itself.

I am really curious to know where you got the LBTR and how it was cleaned? The good stuff from the mudflats might give elevated Alk and Ca levels because it is so easily dissolved. Stuff that isn't thoroughly cleaned may cause some slight pollution. The pH might rise a little which is no problem at all.

Overall what you experienced is a good thing. This indicates that the tank, as currently set up, can maintain good levels on it's own.

whoops an extra 0 got in there..... I meant 2000. When my Mg read at 1800 (switched to oceanic right after dosing and killed a 5 gallon bucket full of milliporas) I was getting reading of alk at 16 and cal at 550.

Thats Why I suggested retesting first and foremost.