Below is some info for your learning and benefit.

How did Ca jump from 275 ppm to 500 ppm? Was it a misreading or over dosing?

The Reef Crystals salt mix is probably not the best one to use right now. Regular IO salt would be a better choice because it has normal amounts of Alk, Ca and Mg. Because the stony coral are struggling right now, they are not using the extra Alk, etc. contained in Reef Crystals.

I'm not sure if I mentioned it in this thread but I learned my lesson the hard way, about fatally sunburning coral. In 2013 I set up Marksreef Coral Farm. It was a series of connected tanks illuminated by the sun through a south facing picture window. Inexperienced with greenhouses, I did something idiotic. I had been growing coral for profit since 1996. I had set many tanks in or close to windows in the past, but never something this intense. 

In this new location, twice a year, for about 6 weeks in Spring and again in Fall, the position of the sun in the sky was such that most of the coral in the system were bathed in direct sunlight for about 9 hours a day. It was beautiful. It was like being at the ocean. I thought I was in heaven. 

My idiotic mistake was not recognizing how water absorbs light. Except for SPS in the surf zone, coral in the ocean are receiving sunlight that passes through 10-30+ feet of water (see pics below). In the major coral growing areas of this ~300 gal coral farm, twice each year direct sunlight passed through only a foot of water before it impacted the coral. Coral started dying, melting away as a brown goo. I knew something was wrong but I didn't know what. Everything I could come up with was done to mitigate the death and destruction . Nothing really helped. It just seemed to have to take it's course and eventually it did recover.

I distinctly remember a visitor who came by and then quickly left, commenting that all my coral were brown and ugly. I racked my brain for answers. I did everything I could come up with. It took a couple months, but the few surviving coral would slowly recover. This coral destruction occurred Fall 2013 and Spring 2014, but I hadn't yet made the connection. 

In the Fall of 2014 my wife and I went on a driving vacation to New York. On our trip we stopped at Tropicorium in Michigan and Tidal Gardens in Ohio It was awesome to meet and talk with other experienced coral growers. **** Perrin, a pioneer of coral propagation had been running Tropicorium for ~30 years. At both facilities, I noticed the greenhouses were covered with several layers of shade cloth. I was told that the shade cloth was to keep bright sun from making the greenhouses too hot and that coral grew fine in this shade. Tidal Gardens actually supplemented with artificial lighting over most tanks. I thought that I was so dang smart. My farm was indoors where air conditioning kept the tanks cool and artificial illumination was unnecessary. 

Upon returning home I found that my coral farm was going through it's third "season of death". I immediately made the connection and dropped the window blinds. Again the last of the surviving coral slowly recovered. Eventually, I learned to adjust the blinds so that only narrow 1/2" lines of sunlight came in between each 3" slat. 

Altogether, I lost around $2,000 worth of coral and over $10,000 in subsequent coral sales. Looking back on it, the worst thing is how I had to endure killing so many coral. 

I hope those reading this find my experience interesting and helpful.

Aloha

Mark