Help for a "mystery"

[frankthirtyspears]

Food evening guys, here with another question, this time about a "mystery" I've been trying figuring out in the last few days...

I've got three autos, in canna soil, BioBizz Nutrients, 150w MarsHydro led, 18/4 schedule, 20-25 °C 39% rh, watered once every 2/3 weeks, in the last couple times I strongly reduced the nutrients since I saw what seemed to be a slight burn, but now the situation went a bit far beyond that.

It all revolves around the yellowing of some fan leaves in 2 of my three plants, coupled with burned tips, very red stems and brown "patches" within the yellow leaves.

My best guesses are that:

1) It Is a light stress issues since i switched my led old 100 w led with the 150 w version and since they flowered they've also gained a lot of height, reaching ~30 cm from the lamp. Also the lower plant isn't affected very much, except for some slightly yellow tips If this is the case It should be fine, i lowered the intensity to 75% and It could be good, but i could be wrong for sure...

2) It's a nutrient problem, in this case i can't really tell, but i suspect either a potassium deficiency (most likely viewing the photos imho) or toxicity. The last couple of times i watered (twice in a week) i reduced the dose almost at 0 since i saw some burnt tips and thought It was potassium toxicity.

Here some photos, thanks for the help as usual!

[WhIpLaSh]

What size pots are they in?

You only water them every 2/3 weeks or days?

[GMO]

maybe just a bit of dry back and salt burn. have them come close to wilting?

[frankthirtyspears]

What size pots are they in?

You only water them every 2/3 weeks or days?

They are in 6,5 lt pots, i water them every 2/3 days (when i feel the pots are lighter basically)

[frankthirtyspears]

maybe just a bit of dry back and salt burn. have them come close to wilting?

It could be, even if i haven't noticed wilting before, just a few burns, spots and a slight yellowing of the fan leaves.

[Bulls]

I think it's Number 1. The LED is a bit close..you should have that distance but in inches.

[frankthirtyspears]

I think it's Number 1. The LED is a bit close..you should have that distance but in inches.

Lowered the intensity at 75% than before, gonna update!

[frankthirtyspears]

Small update: i think i figured out the situation, since the light was very strong, It made the plants suck up all the phosphorus and caused a deficency (i think It should be that 99% since the fan leaves started to purple and some lower leaves started to wither exactly like a phosphorus deficency).

Now i'm definitely going for a heavy dose or Bloom nutrient and a pH check-up, just to be safe (even though using organic stuff It should regolate itself for the most part).