Some salts run 1600 Mg and the Red Sea Mg test has a bad reputation for reading high. Borrowing a buddy's or LFS's salifert kit would be nice data point.
Salt is Fritz, which I can't recall offhand what parameters on that are supposed to be. I don't put a ton of stock in any Mg test really, as I don't think any of them are super accurate. No "buddy" around to test and nearest LFS is over an hour away so...I'll just roll with it for now. If nothing else helps sps color then I'll worry more. I think on the spectrum of things that could be causing issues, Mg isn't as high as some others.