Has Instant Ocean's magnesium level changed?

[Lampshade]

From my experience, IO settles terribly. Water changes at the top half of the bucket were 1100ppm, and I was topping up to 1500. DId this a couple times, was the same, So I kept the same MgCl amount every other water change, then tested my tank awhile ago and it was 1650? didn't make sense, so I tested the IO mix next water change, and it was back at 1500ppm. seems the bottom half of the bucket had higher Mg than the top. Mg tests are sketchy at best though, I use what I measure as a ballpark at best.