Raising Magnesium /w BRS Mag Sulfate/Choride

My Mag is currently at 1280 and I want to get it to 1360-1380. I used the BRS calculator to figure it out and it says I need to use 50oz of the solution in my 240gallon system volume. Am I doing this right? it seems like so much to raise it 100ppm.



I am selecting BRS mag mix solution. this is the correct product right?



It came with the two part starter kit.