Dosing Mg

[Reef Pilot]

My Mg has been running about 1260 ppm lately (used to be around 1400), so decided to start raising it with manual dosing. Yesterday I added 125 grams of Seachem Reef Advantage Magnesium to a 230 gal water vol. This is only 1/2 the maximum dose they recommend for one day. And to raise it all the way to 1350, their dosing calculator says I need to add about 8 or 900 grams, which seems like a lot to me.

So today, I test my Mg again to see what effect it had. And to my surprise, my Mg is now higher than 1500, which is the max I could test for with my Salifert test kit!! WTF!!! It should only have gone up by maybe 10 - 15 ppm according to their instructions.

I reread and reread the instructions, and did more research on the web, but can't figure out what I did wrong.

I also tested my alk (8 dKH) and Ca (400 ppm) and it did not change much from yesterday. And everything in my tank(s) look normal.

I will test again tomorrow. But any ideas what is going on here??