The spots, the upward withering leaf curl, yeah, that's it. Sure, it could be caused by pH lockout, but you were using distilled without a supplement; case kinda closed.
Im with this guy, calcium def takes a while to turn round, like he said run calmag in your water from day one, RO water is not for soil grows. If you have to use RO water you need cal/mag supplement or a fert heavy in cal/mag.
Yep sure it could be pH but i doubt it, calcium uptake is directly linked to water uptake, if the plant dont drink much it dont get enough calcium since it absorbs calcium through passive intake.
Magnesium will not cure a calcium deficiency only make it worse, that is why epsom salts dont work for everyone. Buy a dedicated cal/mag supplement with the right ratios, probably 3:1 cal to mag and use to ppm water to what is needed, that is the way to regulate calmag in your water by ppm'ing it.
Ph lockout is more a myth in good amended soil. Id rather use cal/mag first than get into pH, people seem to confuse calcium or cal/mag deficiency with pH. Ph is an easy way out, getting your nutrients right is much harder and cal/mag will futher help to buffer soil so pH is less of a worry if in fact many growers need even worry about it at all in soil.
View attachment 1731860
Calcium on the left and magnesium on the right, 100% calcium deficiency for this guy, spotty yellow leaves curling up, pH i think not!
Peace