[Delphinus]

I'd consider 1150 to be in the "good enough" levels. I think basically 1000-1100 or above is sort of my own threshold. I think NSW sits around 1300. I haven't seen any adverse effects having it as high as 1400-1500. I haven't tested any higher because it takes a surprising amount of Mg to raise the levels at all so going any higher than that wasn't economical. I would imagine, however, that there is a point where it's too high and could cause problems .. I just haven't empirically tested for the limits.

When I did notice problems with low Mg, I found that Mg was somewhere around 600-700 and it was due to the salt I was using at the time. Not sure if I had a bad batch or a bad brand but it was one of those little life lessons where the takeaway was that you should test your incoming salt from time to time. (One more reason I choose to stick with IO these days: it's been the most consistent for readings out of any I've tried, and if the levels aren't exactly optimal, they are at least the same amount not exactly optimal from bucket to bucket and I like consistency more than I like paying more for salt that ends up being less consistent.. Oops I just turned your poll into a salt talk.)

In particular, when Mg starts to dip under 1000, I first notice that the anemones expand during the day less than they normally do. This I've noticed enough times (maybe 5 or 6?) that I'm convinced it's not a coincidence. And the lower the Mg drops from 1000, the smaller they get. Also, they start expanding again when I start raising the Mg in the tank (I never adjust more than 100 per day, just for the sake of keeping changes slow).

It is the strangest thing, I don't know why anemones care about Mg, but I'm convinced they do.

Not sure it counts as empirical evidence to back the claim, but there have been a few times people would ask "hey how come my anemones don't expand like they used to" on here, I'd usually chime and say "check your Mg, couldn't hurt" and I seem to recall most, if not all, came back and confirmed that they had low Mg levels. So I'm totally convinced there's a connection, even if intuitively I can't understand why an anemone cares about Mg.