We were speaking to the guys at canna about these LED cal/mag issues. The canna nutrient guys are s**t hot when it comes to these things, they have lab equipment that you would not believe and have teams of plant specialists. They reckon that with LED there is less leaf transpiration than HPS. The LED basically is not throwing as much heat at the plant as an HPS does. This affects the rate at which the plants can take up certain minerals with Calcium and Magnesium being the most affected. Hence the need to supplement the cal/mag to restore the balance
Fuck me sideways!
I was wondering what the hell I was doing wrong?!
I reckon that many of LED guys are asking themself the same.
This is some valuable information you should share in LED section on just about every grow forum you are on