I don’t understand why Ph recommendations are so confusing now. For years back in my early growing days it was RW at 6.2-6.3 Ph. The water quality was far from perfect and did lock out at times, but Ca never an issue or deficient. I ran mega gardens and one NFT insert over an ebb and flow table. Having passive systems in the past had too much trouble with pythium and hot res. So using DWC was not an option in my former growing environment. Now that it is I’ve read EVERYWHERE DWC Ph 5.5-6.0, preferably 5.8. So when I filled my res and nutes, I went 5.9 to range it, then the mottling inter-veinal necrosis. Immediately I knew it was either calcium or magnesium, and is my Ph too high ?? Well according to the recommendation it is too high, so again following the recommendation I LOWER DOWN to 5.7. I see it’s getting worse and I’m thinking what Ph makes calcium in hydroponics most available, and I’ll be damned if that wasn’t hard to find a match, but I did and not frequently reiterated. When Ca is deficient in the water, Ph SHOULD NOT be below 6.2. Well fuck me WHY couldn’t this be more discerning instead?? I’m mad, cause there’s growers on the net publishing false information by not considering Ca content while recommending a passive Ph range that will trigger deficient uptake. Far too much misinformation about passive hydroponic Ph going around without adding this caveat, and it’s been maddening to deal w. I swear some people have no business thinking they can write recommendations for growing cannabis without figuring different scenarios before putting out “their wisdom”…sheesh!
Agreed. Too many variables to consider when understanding nutrient uptake ranges and ph. It’s best to swing it from 5.5ish-6.5ish to mitigate deficiencies but then that brings in a whole new set of problems. There are auto ph brands, but that’s something I have issues with. The charts we all go by to understand it contradicts what they offer. No one ph level is perfect for a plant, it needs a combination… Maybe I’m wrong but until that is fully understood and solved, organics will be superior. We just don’t know enough in my honest opinion. I chased deficiencies left and right during my DWC days. 
When I run rdwc systems I like my ph at 5.9 on a fresh res. I Top up with half strength nutrients at 5.6-5.7 ph. The ph will usually raise slowly throughout the next 10 days to 6.3.
Rinse and repeat.
In veg
Cheapo A+B nutrient at ~650ppm
Touch of potassium silicate
Good to have epsom salt and cal mag on hand
In flo
Week1 veg nutrients
Week2 50/50 veg/flo
Week3 and on
Cheapo A+B ~900ppm
Week4 slight pk13/14 boost 1100ppm total
5 900ppm
6 800ppm
7 700ppm
8 500ppm
9 300ppm flush
Flawless nuggage every time
There should be plenty of calcium throughout the grow as is. some strains can benefit from 1-2ml/l calmag, maybe 
I ran very similar ppm’s to you on my last run in RDWC and had minimal issues. Maybe a cal mag problem but maybe not lol still learning. That was with 2x 600w hps/mh lights but still I think it depends on alot of things like light intensity/temps/humidity/strain so many variables best to figure it out for yourself lol
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 
Half of what’s on the books attributed to acidity is calcium or carbonate antagonism. Unfortunately weed growers, contrary to their protests to my claim, believe the accepted narrative of literally everything they hear from more than one person (or the right slick haired tight shirted expert), and boost the flaws misunderstandings oversights and general bad science to 11.
You’d be a moron to trust 100% of what someone says on weed grower forums. Unless they show you their chemistry badge.
Interesting responses! My main gripe is “recommended” Ph of hydro between 5.5-6.0 WITHOUT considering what the present calcium of tap water is in that location.
I think we can all agree highly calcified water leaves a salty crust behind. I have a stainless steel cat fountain, and water in 2 locations used showed that crust on the surface, but where i am currently that’s lighter, so it tells me the water is calcium deficient. I think in some cases, a simple cal-mag of 1-2% isn’t enough. I’ve had to go w Blue Planets cal-mag pro at 15%, and now that I have along w a Ph above 6.1-6.35 range all new growth is perfectly healthy.
A grower that recommends ranging from 5.5-6.4, I don’t have issue. There’s enough discrepancy for calcium present, even failed to being mentioned. Where I have a problem is disregard and being adamant of Ph under 6 generally for hydroponics, and clearly I’ve learned and seen this is patently false. Seriously some of these people are going to cause more problems for those researching about Ph than helping them. We know Ph is dependent on nutrient availability to the plant and suggesting a lower range that may be lockout at the highest end of 6.0 is telling the reader DON’T go above it, then that reader will think it’s something else and not the Ph and ramping up ppm in effort to correct…BAD INFORMATION.
I said when reading around I found the emphasis of not going above that 6.0 more often than being ranged, and consensus does factor in decision making psychologically. It took me two weeks to figure this out when I could be closer to flowering instead. For another new grower it could be much longer to realize they have to be over 6.1-6.2 to fix the lockout/deficiency they’re experiencing
IDK where the 5.5 comes from. My plants would go full yellow on me at that range.
I don’t ever go lower than 6.0, ideally 6.2-6.4
My water is rock hard. 350+ppm