All good suggestions. I have to agree with the first in some respect.
I've got two tracks going in my mind:
A. A slight Mg deficiency compounded by bright LEDs.
B. An Mg deficiency you remedied, then you locked out potassium.
Then there's the third track:
C. I took two, totally wrong wild stabs.
Your on track, and well could be correct, I'll try and explain below my line of reasoning.
What are your roots like Frank? Or Phosphorus if not roots.
Correct also, and the same. It's both actually, IMO.
Possible, but highly unlikely. I've had pretty decent control over ph, although it's a possibility on some level yes.
So here's my line of thinking on this one. Calcium Excess is the culprit, and maybe a little too much light, as was also suggested. I was certainly pushing them hard and fast with the LED's.
But I have started using calcium hydroxide to balance my pH, and if I'm correct here, that's the culprit. It's attempt at pushing the calcium out of the tips...
Too much calcium can lead to severe consequences. The most obvious problem with
calcium additive is leaf burn. The cannabis plant is reacting to excessive Ca+ and is trying to push it out from the leaf tips. This causes necrosis (death) of the tips, they will turn yellow/brown.
Besides causing leaf burn, excess calcium doesn’t actually create symptoms as a deficiency. Instead, too much calcium actually lead to
problems in other nutrients, such as magnesium and potassium. This situation is a frustrating problem. Too much calcium will lock out magnesium or potassium, the only way to correct is by first dealing with the calcium issue.
So, you’re experiencing potassium and magnesium related symptoms, the actual root problem is too much calcium. Excessive Ca+ doubles or triples your work by making it necessary to try and
fix your magnesium and potassium issues. It can you astray chasing other nutrients, while Ca+ remains unresolved.
I'm changing up, so lets see if this comes around or not. Flush a little, then same mix with only single adjustment. Instead of balancing with calcium hydroxide, I'll use a little potassium hydroxide this time around.
Things look a little greener in the core today, also appears a bit more engaged, so I'm encouraged.