I'm circling back to Gypsum again and have gone away from Cal Mag altogether. Growing in 20 gallon pots and have gone full organic, as much as I can or understand about it anyways. I agree with what some have said here about "getting it right" from the get go when setting up your grow, and from what I can see, this old thread was aimed at or attracted a lot of farmers. Interesting. As mainly an indoor grower, not sure all that's been said here applies? But... I do have a problem pot. Easiest thing to do is to dump the soil and start all over. (with that one pot) In the middle of a grow and nearly a month from harvest, that's not gonna happen anytime soon. This is where I can see using Gypsum can help. It's more soluble than lime. And I believe from my readings, available to the plant days after adding? Another reason I decided to get away from cal mag is that my plants in general from this problem pot have only been showing calcium deficiencies. Seems like Gypsum is perfect in this scenario.