Nute burn, Light burn, or something else?

[Geeza]

Hi Everyone,
Can anyone please help with identifying the problem here? The instructions on the nutrient bottle advise to get the EC between 1.8-2.2 for my plant which is 4weeks into flowering, so I got it to 2.2, A couple of days later noticed the damage (that was 2days before this pic was taken), I immediately refreshed the rez with nutes to 1.6 EC and then turned the light down to 60%. As the leaves were already damaged I didn't really expect any change there, but just hoped to stop it worsening.
I'm in a DWC system, led 480watt light at maximum but around 2-21/2 foot above the canopy, and I still really don't know what the issue is/was and could do with advice from you experts out there?
thanks in advance for any advice.

[dirtymike]

Heat and light stress with PH issue with iron deficiency

[Geeza]

Temperature is fine, light, pH & EC have been amended to the appropriate levels. I always maintain a pH of 5.5-6.2 when refilling the reservoir; however, since shifting to a new nutrient, I have occasionally noticed pH fluctuations, typically a few days later. When I see this, I will amend. I've now made it a point to check pH & EC daily. I previously used a different nutrient that was stable and problem free but it no longer exists on the market. So, I got this new nutrient that advises an EC of up to 2.2 would be ok, but after seeing Bluey's comment, I'm now looking at this EC of 2.2 as possibly an issue. Will also check iron now that you mention it.
Thanks for your input Mike.

[golfnrl]

What's the PH? Does it fluctuate?

[golfnrl]

Sorry about that. I read the wrong comment. I think you're right though, about the potential problem being the higher EC. I'm curious about the PH fluctuations and how they present on the weed. Perhaps you have some thoughts. What constitutes PH fluctuation? Does it mean a radical shift all at once? If so, what is a radical shift? Or does fluctuation mean the PH drifts a bit out of range? What I read says PH should be stable. To me that means constant or the same all the time. Yet, I have also read that as long as the PH is in the range for whatever the grow medium is then that is OK as well. I'm trying to learn more as I have been having PH issues and it seems that most plant problems start there.

[Geeza]

The pH and EC fluctuations I'm experiencing, I believe, are due to the new nutrients I'm now using, as my previous nutrients never had this issue. They would nearly always be stable, or if they did fluctuate, it would usually be subtle like a few points either way, (pH), and more like 5 days after a reservoir change, which I thought was normal, as the plant would take up whatever it required at the time, causing the fluctuation, (which, y'all can correct me if I'm wrong, is how I understand what constitutes pH fluctuation).
I got used to this stability, hence why I think I got complacent and seldom checked pH or EC daily. Now these new nutrients seem to fluctuate radically (like say from 5.8 to 6.8, EC also +/- ) and in a matter of a couple of days. I'm certainly not happy now, as firstly, the nutrient bottle says an EC of up to 2.2 is fine, and secondly, I find the instability of it not only annoying but also costly. As far as how pH fluctuations present in the plant, I'm no expert, but I understood there are all sorts of unpleasant symptoms and damage it can cause if the fluctuation is extreme, meaning beyond the required range. ( I now think this is what's happened in this case) If there is a fluctuation within the range 5.5-6.2 (hydro), I believe this is a good thing. I think problems arise if pH fluctuates beyond the required range. I reckon I've got to find another nutrient that is good and stable. My thoughts only, I hope that if I'm wrong, our experts here can set it straight for those of us who are curious or unsure. Hope that's helpful for you Golfnrl,

[golfnrl]

Geeza Yes, very helpful. Thank you. Just to be clear, you're thinking that PH fluctuation within range is OK. That sounds normal to me as well. I re-read that yesterday from a January 2025 update to Nebulas' grow guide. To me this means that PH fluctuation within range for the grow medium is OK, outside the range for the medium, not good. However, a plant may tolerate a point outside the range without adverse affects showing or stunting growth but it's still not good. And anything over a point out of range will cause plant problems and the plant will most likely show them.

I have a rez in the autopot system I use. Everything you describe as stability sounds similar to my feeds, EC, PH etc. My plants in what must have been (did not check PH in the pot's tray at the time) outside of the normal PH range have presented as stunted with beet top curly virus looking symptoms, mottled leaves, small buds, etc. There's a thread on here somewhere about it. I know PH is critical to success so having one plant with an issue while others on the same feed schedule didn't is/was puzzling. I normally maintain 5.8-6.2 in the rez. But the rez in my system actually needs to be maintained 5.5 -5.6 to give the proper PH range in the pot's tray. Example: I had the rez set to maintain 6.1, that measured at 6.4-6.5 at the pot's tray. Not good, but not so much of a problem when I have it set at 5.8 but it appears I was causing my own problem by not regularly checking the PH in the pot's tray. Lesson learned. I'm still uncertain how two plants on the same system that has PH fluctuations can each grow differently, genetics maybe, IDK.

Good luck in your quest to find different nutes. I use CX Horticulture nutrients, full line. Very stable and easy to use. They grow great weed when the gardener has his head out of his...oh well you know where that was going.

[Bluey]

I'm not sure its light bleaching. Is it typical to loose pigment like that? Light bleaching hits the entire leaf in my experience. I think the pics white balance is way off so it's stuffing up the colours.

I can see signs of typical nute burn but its not that bad unless what we are seeing along the leaf edges is also nute burn, but it doesn't look typical to me.

An EC of 2.2 will burn everything I have grown in coco so Im going minor burn with nute lockout....check pH. Lowering EC and PPFD helps too.

[Bluey]

Correct pH & EC should sort the lockout. What week since flower started? Around week 3 to week 4 I stop calmag and switch to PK, typically. Sometimes I have to start earlier though depending on N levels

[Geeza]

coming up to week 5 now, and yes, I stopped Calmag and use PK around week 4 also,
Thanks

[Geeza]

What I also don't understand is why the damage has affected the leaves at the top only. To me, the edges and points of the leaves below appear more like nute burn, and the top more like light burn, but I'm not convinced it's light burn.

WOW!!!! I just realized there's something I had completely forgotten about.
Before this leaf damage appeared, I had done a reservoir change, and I noticed mould beginning to form on the roots in "the air zone". I mixed 17 ml of 3% hydrogen peroxide with 1 litre of water and sprayed the mould, which disappeared almost instantly. I then rinsed/splashed the new mixture of nutrients (that I had already filled the reservoir with) over the roots and left it. I now wonder if that's what's caused the issue? Burnt roots, maybe? At the same time, I did this to 3 other plants as a precaution, but no adverse reactions from those 3, I guess it's possible I didn't spray/dose as much as the moulded one, as the others had no mould? Your thoughts?