If you think its just calcium some simple "cal mag" could do it, a lot of companies make this, I use botanicares. like $20 for a liter or $50 for a gallon at a hydro spot. I actually had the same thing myself just last week, but I usually give half veg, half flower nutes last week of veg, I didn't this time because I completely switched my nute lineup and my veg and flower nutes weren't the same so I was unsure of how much to give, but once I gave it the first full flower dose of nutes, it stopped.