Have you calibrated your refractometer lately?
How old are your lights? Spectrum shift?
Like previously mentioned, raise Alk up and keep it stable.
I don't use a refractometer, but a swing arm hydrometer. It has been pretty steady at specific gravity 1.025 on both my hydrometer and a friends. I thought about getting a refractometer, but thought even if my salinity was off by a few points in either direction I'd be Ok as long as it's stable.
That's another frustrating thing about this. The friend who's hydrometer I borrowed is completely new to aquariums. I helped him set up his first tank, a 58 gallon reef tank and showed him the ropes, and his tank is doing great. Overgrown with soft corals, and using all the techniques that
I taught him! He's actually doing less work than I am because I'm doing so much testing and he just throws stuff in the tank and it grows.
As far as lights, they are LEDs so I don't think they spectrum shift. I thought that lighting could be an environmental issue, but I don't really know how to be certain without having a PAR meter and I really don't want to start acquiring any more gear for this project. I've never met another reefer that actually has a PAR meter. Anyways, the lights are a pair of Hydra26 LEDs which are standard on the specific aquarium I own, a Red Sea MAX S400. I downloaded the settings that several other prominent soft coral keepers have been using. this adjusts the color spectrum throughout the day.
The alkalinity problem will be addressed soon. I re-read the replies I've received in this thread and that seems to be number one, or close to it. I didn't;t think it would be as critical for soft corals, but we'll have some more data soon. I plan on slowly increasing dKH with baking soda starting tomorrow and monitoring Alk and Calcium.
Thanks for your input.