Magnesium dosing limit

question for u experienced reefers. So my mag reads 1180 and i want to get it to 1350. I have put 50ml a day and after 3 days i am still at 1180. I thought something was wrong with my red sea test kit so i went to my LFS to have them test... the guy at the store said I shouldnt be dosing in ML. I should be dosing by cups. is said 50ml will not make a dent and if i really want to get it up i need to add 16 ounces a day. is that insane or does that sound right to u guys? the bottle says i shouldnt add more than 50ml a day. yet the guy at the store says 50ml will do nothing to my tank. after 3 days he seems right. I looked at the calculator and it says i need to add 708 ml to achieve a 1350 reading. he said i can do this in 2 doses lol.

Anyone else dose Magnesium over 50ml one shot?

thanks in advance.