Please help can’t figure this out

[oneluv0027]

Good day everyone, I’ve been dealing with an issue and can’t seem to get a grip on it. Possibly because I don’t exactly know what the issue is. First time I grow in coco, first time I try to scrog and first time I use LED for Veg. I did notice it more after I switched to my hps but after doing a bit of research I found out it could be a range of things. To my understanding, it could be a ph issue, salt build up, a watering issue, a heat/light issue or a phosphorus deficiency. I flushed with a mild solution, I moved the light a little further away and I just switched to 12/12 so I added the phosphorus part of the feed two days ago and it isn’t improving yet. The EC of 0.9 is the same pre-feed and in the runoff. It’s mainly on the older leaves and it starts off as dark blotches and ends up brown, rusty and dry. The humidity in the tent stays between 40%-55% but one issue I noticed is the temperature fluctuation. When the light is off, the temp is 21 Celsius and when the light is on, it’s goes up to 27. Any help would be greatly appreciated thanks ahead of time. Ps. It’s only one of my 4 plants that have that problem but the other ones look a little droopy for my liking.

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[DanC520]

Using cal mag in your feedings? That looks like calcium deficiency to me, give a google and see if agree. I know I charged my coco with cal mag before potting and use in every watering. I've read its used up faster under LEDs, but in passing so can't confirm.

 

[oneluv0027]

Thanks for the info, I have been using CalMag with every feed and the internet led me in that direction as well. It said calcium issue or potassium issue. The coco I’m using was supposed to be prebuffed and I didn’t have this problem the first 6 weeks of the plants life or I didn’t notice it as bad under the LEDS.. what I did notice yesterday after feeding though was that the runoff ppm was almost 300 parts higher then initial feeding and what’s worse is now it’s starting to affect one of my other plants. I’ve read many posts on here about similar problems and the issues ranged from CalMag/, potassium or even manganese deficiency or over/underwatering or salt build up to not enough oxygen in the medium. I debating now if I should do a flush with a mild CalMag solution but not sure if it’s a good idea since my issue could be over watering. Thanks for the advice, I’ll figure it out, hopefully lol. I’ll let you know how it goes.