@Growmau5, Well it's really a given that led lights will decrease calcium uptake specifically. Calcium is taken up relative to the evaporation and with led you have less heat on the plants than from HPS, ergo less evaporation and therefore ... less calcium uptake.
You seem to be "overdosing" your plants on calcium and magnesium (both elements on the periodic table) so you won't see calcium deficiencies obviously, but you must be able to understand that that makes you one of the least qualified people to make statements about slight calcium deficiencies caused by lighting differences.
People who dose their extra Calcium in more frugal amounts, or like me none at all while using HPS lights, can notice this effect.
I agree that it's only a small diference, but it's "bullshit" (to quote you literally) to pretend there is no effect on calcium uptake. Depending on the strain you might not even notice an issue when just using the basic nutrients, but it simply is a fact that with led you have slightly lower calcium uptake compared to HPS.
I would like to offer some testing that I believe pertains to the OPs question. I recently finish a series of videos evaluating 2 nutrients lines:
-one with a multiple bottle liquid line offering me full control and the ability to dump a "random shit load" of calmag into my feed solution
-the other line was Jack's 3-2-1, a line used and documented by thousands of cannabis with a host of lighting technologies.
-I never deviated from the 3-2-1 ratio which appeared to supply adequate levels of calcium and magnesium. with no alteration or additional additives
and it is the SINGLE MOST FRUGAL hydroponic nutrient on earth.
-with all variables controlled, the result was nearly identical.
HPS, T5, CMH users across the world are successful with this system at these ratios. I am an LED grower and I was successful with it at the same ratios. I think the question becomes, what kind of nutrients are the led growers claiming "calmag" deficiencies, and how qualified are they to distinguish calmag def from nute lockout or burn.
Bringing this whole thing back to the OP.
Based on all the experience people have gained on there forums using various DIY builds. What are the biggest challenges in switching from traditional grow lights to white COBS.
Most importantly what are the biggest changes in nutrient requirements.
Simply "switching" to LEDs is not enough information to elicit the response "add more calmag" that is my point here. And yes, generally I think this recommendation is bullshit. read the plant, monitor the enviroment, and understand what is actually in all the pretty bottles from the hydrostore, then respond to those needs accordingly. like Wietefras said, Anything that slows transpiration: high humidity, cold temperatures, etc can induce calcium deficiency even if the calcium levels are normal in the growing medium. so if your room is running colder due to a "switch to LED" the last thing you would do is add more CALMAG!
As far as being qualified to talk about the calcium needs of organisms, I spent 3 months on a research vessel studying the deposition of Calcium carbonate in invertebrate marine organisms. so im pretty familiar with how it works within cells, photosynthetic or otherwise.
with that said , i do understand your perspective on: if you are always overdosing, how would you ever see a deficiency. my response to it is, what is the benefit of running an important element like Calcium so close to the razors edge, that you almost become deficient. its very inexpensive, easy to obtain, comes in a variety of forms and aids in so many processes in the plant that that we should be saying NPK.Ca
