Super low magnesium in salt

[Millz034]

So long story short I bought a bundle of stuff for saltwater decided to use the salt I got in it not realizing it was super old and I live quite a peice from any LFS the magnesium levels are 1090 to 1120 the first batch I mixed up was 1300 now every batch comes out 1080 to 1120 I have corals in the tank it's been up for 3 months fully Cycled started doing water changes that's when I noticed my magnesium going down.
I'm just wondering will the couple coral I have be alright until the new salt comes in the mail in about a week I have 2 blastos a couple hairy mushrooms and a ricordea Florida
Its a 20 gal. Cube
Also got 2 clownfish and a CUC

 

[TD82cat]

I wouldn’t worry too much if they have been doing ok up until now. Another week shouldn’t do much if any damage. Obviously they would fare better with correct mag levels. Or you could dose magnesium if you have on hand