I guess what I’m trying to say is that if you’re seeing calcium problems it’s probably present in sufficient quantity but locked out 
In my previous post I added my preferred ppm - the emphasis should have been on keeping it simple and frequent res change… in hydro less is more as you know.
When it comes to humidity if it’s too low -fix it, if you can’t, adjust your soup accordingly.
With lower humidity comes higher transpiration rates and faster uptake of nutrient rich water. The goal is stability… plants should eat as much as they drink. Once your water level has dropped, ppm should still be the same etc
Humidity too low = drink more = lower ppm
Humidity too high = drink less = higher ppm
Environment, lighting and strains change, principles don’t.
There’s tons to be said about hydro, I started straight in rdwc my first indoor grow and after years it’s become second nature.
You should see my soil grows tho hahaha I’m a total noob in soil and everybody tells me it’s easy
Student for life 