if you have to use cal-mag, it's a crap fertilizer, imo. a hydroponic fertilizer or system should be complete. you shouldn't need to add a supplement at a certain point, it should be provided at proper concentrations from the beginning and at all times. it's a sign of a crap fertilizers, if not. if you run into a rare seed or clone that just requires a little extra, then that's a great reason to use cal-mag or similar... or, just up the Ca in the part of your feed that contains it. get a 2 or 3 part system that provides everything. prefer dry over liquid, because it saves tons of money and stores a lot longer... virtually endless from our perspective. if it has a cartoon graphic or solely marketed to pot culture, it's probably trash, lol. like even now, you have somethign goin on, but it isn't a calcium deficiency. it's a toxicity of some sort or lockout due to a poorly balanced feed. they do it on purpose so your ocd kicks in and want to do 12 things to fix it when all 12 likely make it worse, lol.