I think Don to be sure send a sample to each of the same sample. Me thinks things are not well over there at AWT. People have had their ca, alk and mg levels be way off at times but that may be the reefer and not them, hard to say. Give AWT a shot but test the sample yourself with your kit/s for a comparison. There are two things to remember with these test, same for Spectra, so ask her.
1. Ca++ and Mg++ more than likely are done with ISE probes, AKA PinPoint Calcium monitor, using a ISE probe. Spectra more than likely uses ICP, don't know so ask. It is much better.
2. Alk is a different beast and is done by titration only. What many do not know, so ask Spectra, are they titrating their sample to the Alk seawater pH end-point, which is lower than the FW end-point of Alk. If not you Alk is actually ~ 10 % higher. Seawater is ~ 4.2 and FW ~ 4.5 pH