Advice? Polyp Bailout ??? What the...........

I am learning all kinds of terms and finding issues that can occur with reefs. I had a Duncan coral I got at Springfest. Had one large head and three small ones growing. The big one was happily swaying in the current, next thing I know it's floating around the tank. The day later the little ones follow. Now I have a bare stalk.
Parameters have been stable, temp right at 78 with controller and fan.
I just upgraded lights, was it too much too soon? I also started kalkwasser in the top off after I got parameters up with BRS two part.

29 Gallon Biocube
Calcium - 490 (red sea)
Alk - 155 or 8.6dkh (hanna)
Mag- 1400 (red sea)
Salinity - 1.026 (refractometer)
phosphate -0 (elos test kit)
nitrates- 5ppm
ph 7.8 - (need a better test for this- going to get probe for reefkeeper)
GFO in reactor
5 gallon water changes weekly

Been running almost a year, no fish losses, no algae problems, a little cyano.