HELP! Scabby leaves and some turning black between veins & red stems (petioles)

[Canucklehead]

Geez everything was going great until I lowered the 250w (at the wall) led a week or so ago on my potting mix grown sativa. I noticed the leaf edges curl up a bit after a few hours so I moved the light further up but now the upper leaves are turning brown but only on one side of the plant and there are similar but less obvious symptoms on another smaller plant in the same grow area. It's currently 4th week I have this one and it was a foot tall clone when I received it. Repotted 2 weeks ago and watered in to settle the new potting soil at that point. Since then watered once with about a litre of water with a small amount of generic nutes since the potting mix has some organic material in it.First 2 pics are of the sativa leaves with the brown and some black spots which I assume are going to be brown in a short period of time. 3rd pic is of both halves of my sativa 'manifold' showing that the other half is not showing the same amount of destruction and the last is a pic of an indica that is exhibiting some of the same 'symptoms'. Using 18/6 lighting and the led is 'full spectrum'. I used this light once before and never had an issue with some autoflowers last year. Does this look like a light burn issue or a deficiency to you more experienced growers. PH in the grow bags is 6.9 or seven depending on which of my 2 meters used and I have only used PHed water/nutes (6.2).Any opinions or advice is greatly appreciated. -Bill

[Willyd]

kind of looks like potassium deficiency

[CaptainWiese91]

Have you checked your ph ?? - ohh yea you have.
but the soils ph is too high. Potassium can’t get absorbed if it’s 6,9. They want much lower levels

[Canucklehead]

OK great 1 000 000 thanks I'll look at ways to reduce the soil PH ... do you have a go to method ?

[CaptainWiese91]

Maybe drop the water a little lower than you are use too. What kind of Ph meter you got ?
Mine I can stick in in the soil, and it will tell me the PH in the soil - and also the temperature

[Canucklehead]

I have two of those types of soil meter one digital readout one probe and one analog two probes. Both show the PH at 7 ish as mentioned. Just ordered a pen type PH water tester so I will hopefully get more accurate results than the test strips (for my pool).In the meantime I'm looking at lowering the PH on my next water/feed although I think I'll do a 'flush' in this one grow bag asap. Just need to research what additive is the best DIY PH down(citric acid ? cider vinegar ? ???)

[CaptainWiese91]

I use an organic lemon, cut in half and pressing the juice out in a bowl, then I put a little in, waiting 20 min, look PH and if more is needed I do it again.
My bottles are 5,6 liters - after all my nutes is in, its around 6,9 i always lower it to 6,1-6,4. Using almost half a lemon (in juice)
But it all depends on the water and nutes of course - só you need to make some experience of course

[CaptainWiese91]

I have a lemon and a lime tree in my garden, so I know it’s completely organic

[Canucklehead]

Well thanks again for your help. You are very fortunate to have the citric acid source in your garden. I, unfortunately, had to improvise so I used apple cider vinegar and I have not seen any substantial change in the readings from my grow bags a few hours later so I will keep an eye on things and do another flush with lower ph water in a couple days if need be.

[CaptainWiese91]

Good to hear 👍🏻