Help diagnosing problem during flower

Hey all, so I started noticing some sort of deficiency/lockout/toxicity problem around week four or so of flower and cant quite figure out what it is. I had thought I fixed it, but it started getting worse towards the end of that week, and I'm into week six now (day 37) and its looking much worse. Initially I thought it might be a calmag deficiency since I switched over to a new COB light that I made to replace my old T5, and the overall light output is much greater. So thinking it was cal/mag deficiency I added 5ml/gal of calmag to the res, and also mixed a quarter strength batch and did a foliar spray for a few days.

After it started getting worse I thought maybe it was some sort of nute burn or lockout due to excessive salts because my ppm was a tad on the high end at 1500 (on the t5's I was running around 1000-1100), so I flushed the system and ran pH'ed water for 24 hours, then added back nutes to a much lower level around 900ppm, and has now been running at this level for about 3 days.

It's possible the flush may fix it, but I still want some opinions of what it could be exactly. In the pictures you can see what appears like cal/mag deficiency with the rusty looking spots, but at the same time you can see leaves rolling in like a canoe, and some are overall starting to turn brownish/reddish in hue.

I'm running 8 COBS at 50w each at about 10-12" from the canopy which is reading around 80k lux on my lux meter, can't remember what that roughly converts to in ppfd. Nutrients are GH Floraduo, Calimagic, Botinicare aquashield, EWC tea added twice a week, floralicious+ as well as some mammoth P I got for free. pH stays between 5.7-6.0 and water temps stay at around 66f.

That right there at first glance is a Potassium burn. Too much K. around week six is a highly likely time to develop toxicity . That flush may have been just what the doctor ordered. But damage is done already. And I thought for a moment you had mites...tiny little specs on the leaves that are viewable from the top. but def K overload. What is your grow media?

Looks like you may have spider mites.

SwitchHitter said:

That right there at first glance is a Potassium burn. Too much K. around week six is a highly likely time to develop toxicity . That flush may have been just what the doctor ordered. But damage is done already. And I thought for a moment you had mites...tiny little specs on the leaves that are viewable from the top. but def K overload. What is your grow media?

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That very well may be the case since I was running higher ppm than normal this time around. I'm hoping the flush will prevent any further damage along with the reduced ppm. Definitely no spider mites here, I did a thorough check with a 30x loupe as well as checking a few leaves under a microscope at 120x, it appears to be strictly nutrient related. I'm growing in hydroton in net pots in a 25 gal rdwc loop.

I should also add that the damage only appears on the top leaves exposed to the light, fan leaves further down under the canopy look perfectly fine and green.

Sureshot2 said:

That very well may be the case since I was running higher ppm than normal this time around. I'm hoping the flush will prevent any further damage along with the reduced ppm. Definitely no spider mites here, I did a thorough check with a 30x loupe as well as checking a few leaves under a microscope at 120x, it appears to be strictly nutrient related. I'm growing in hydroton in net pots in a 25 gal rdwc loop.

I should also add that the damage only appears on the top leaves exposed to the light, fan leaves further down under the canopy look perfectly fine and green.

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When I was running a RDWC, ALWAYS kept my ppm under 1300. honest to god you'll do much better with a lower ppm in dwc. they say you can use a quarter strength you typically would for any other hydro system. In a ebb and flow I only go to 1500

SwitchHitter said:

When I was running a RDWC, ALWAYS kept my ppm under 1300. honest to god you'll do much better with a lower ppm in dwc. they say you can use a quarter strength you typically would for any other hydro system. In a ebb and flow I only go to 1500

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Yeah I normally wouldn't go that high but I figured "hey I got this bright new light maybe I can go higher ppm"... I guess I learned that lesson the hard way lol. I figure I'll just stick with similar numbers that I used with the t5's.