What could this be?

I’ve been growing this strain for about 3 years now, and never had this problem using my MH/HPS bulbs! This time I used an LED light for the first time and this happened? Any thoughts on what this could be?

High powered LEDS cause problems with Calmag usage due to the uv or far red (can't remember which one) I think it's UV.

Keep them lights a bit further away and up your Calmag for a few feeds should solve the problem.

Happens to me and alot of other get caught same way.

^ Yep , I had that same issue the first run with my COB LED light, Double the Cal Mag, It'll fix it ......

EDIT: for some reason it didn't save the 2nd part of my response.....

If the lights are powerful enough you'll end up using more of all nutrients because the lights are giving more ppfd that is available to be utilized by the plants thus requiring more nutrients then you would use with a different kind of lighting

You can also add 1ml per us gal of unsulphured molasses during veg to help substitute your Calmag. This is due to molasses having a Calmag content. This also helps feed any beneficial bacteria enzymes and fungus found in your root zone.

Another good tip is to introduce if you haven't already some form of left handed or L-Handed amino acids. These does a number of things but more specifically in this case they help open additional ion channels that help with the uptake of calmag.

Silentvirtue, and Budget Buds,.....thank you very much for the information, it was very helpful!