I've found that to be accurate. I use straight FNB, and if I see a mag or cal def moving in, I'll throw in some molasses, clears it right up. I also start running molasses always starting at the latest about 4 weeks of flower.
I do have some Cal-Mag that I picked up to try to combat a def that got through the molasses, but that turned out to have PH as the cause. Now I'm right back to straight FNB, the flower room will start it's regular molasses run this week.
1 Tbsp per gallon, plants love it!
Current vegroom: Recieved Molasses regularly first few weeks.
Last round flowered, with molasses
I highly recommend it, but having some Cal-Mag on hand is a good thing, for that one freak strain that needs just that touch more.