Identify problem marijuana leaves

how do I lower the PH

Check out this thread: Lowering the pH of my water

Hi I too have a problem with just one of my plants the two lower main fan leaves have turned to this…Could someone please help me? Thx. .

Same advice as above, it’s probably pH. We need to know the pH of your water, and of the root zone.

yes it has crossed my mind but I have 8 going all have received the same water and nuts but its just my one WW thats showing this. its a soil set up, getting litmus paper tommorow will let u know whats ph at roots and upper soil level. thx

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Also, check out Latewood’s support ticket check list, maybe you’ll notice something especially relevant to your situation that you haven’t thought to mention.

Also just having these detailed parameters of your grow could help us identify anything else that might be contributing.

Macstoner thx for advice, whats the link for that support ticket thing mate? I checked my PH 6.5 going in, run off 6.3, and getting between 6.1-6.3 form the root area. I think it could have been a bit of mag loss, been putting cal mag in all of them but I think by accident I did not give my WW much, need to get more organised, got meself a white board and pen now, going up market now. Finding it hard now the summer is kicking in over here UK keeping my temp at 75 deg, keeps going upto 80, sometimes 85, I have two fans one osc at bottom pushing C02 up one at top running over my 600w hps, a 5" extractor fan to carbon fillter and a 4" fan pushing fresh air in but have to keep opening door all the time, might have to switch to a night time 12 light and dark day time i think, but cant really do it now as im in flowering mode all ready made one time error by my timer going tits up and gave them 16hrs of light in early bud but i gave them some rest and switched timer and seem to be coming on fine. any advice about how to change to a night time 12 light would be helpful tho guys. thx

The support ticket is like a checklist of all the parameters that might be in your grow. For example answering all of them might help us see something we were not aware of in your grow that might be a contributor to your problems.

Like knowing what nutrient system you are using and at what PPM’s could help confirm or rule out a cal/mag problem, but it seems you might not be following anybody’s nutrient system, or if you are, like you said, maybe you forgot to give that one as much, which confuses me because usually most people or nutrient systems I’ve seen all have you mix all nutes together in a large container, have them stabilize and tested for pH, and then that is poured onto the plants so everyone is getting the exact same stuff.

Anyway, it seems you identified the likely cause of the problem, sometimes filling out the list helps us get there quicker and sometimes it doesn’t, so it depends on whether I point the link to it, sometimes I do and sometimes I don’t.

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Can anyone tell me if this is burn or deficiency or what?

It looks mostly like burn, but if you are feeding a balanced nutrient and are sure you are not over feeding, it might be a deficiency or “lockout” due to pH.

I’m betting mostly it is nute burn, or an accumulation of too many nutrients in the root zone.

A pH and EC/TDS reading of the root zone could help us help you, maybe of the runoff after feeding with pure water. Or watering only without feeding, rather. Testing the run-off water will give us a general idea of what is going on in the roots zone.

you can also test your soil as described here in Robert’s blog:

check out these tools if you haven’t already done so:

hope this helps,


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macGvy: would a PH issue cause rust-brown spots to appear on leaves? Have my PH at 6.2, but I ran out of vinager, so the last 2 waters have been 7.4 (which is what my well water is from the tap)

TIA for your advice.

would a PH issue cause rust-brown spots to appear on leaves? – Yes, yes it most certainly can.

It looks exactly like that is what is going on in your garden.

Check this out:

Hope this helps,


Thanks for your advice (: Do you think Sul. Acid works better than vinegar? Thanks Again for your help

That is exactly what I said in the other link. Vinegar is not a very good pH down at all.

Thanks, I missed the Sulfur. Acid link…Got it now…Thanks Again for your help. Much appreciated

I am growing a White Widow in its 8th week of flowering. In the last 5 days some upper family leaves have been drooping and turning yellow with brown spots. Also some of the leaves around the Cola have done the same thing. I cant raise my LED lights any higher…any suggestions…Is this a nutrient deficiency…toxicity…light burn ??


It might be light burn, but light burn is more of a fading, if it is from photo-inhibition and not an actual heat burn.

Especially as you mention the yellow with brown spots. This sounds more along the lines of a toxicity, maybe pH or nutrient salt toxicity and deficiency. Often pH not only can make some nutrients more available (even to the point of being toxic) while also making others unavailable, some nutrient toxicities in and of themselves can cause other nutrients to be locked out. Sometimes even without the pH being out of whack, some nutrients can build up to the point of creating a toxicity, this is why many growers periodically flush their soil.

I’m not convinced it is light burn, a picture could help, and any other additional info, such as pH numbers or TDS/EC numbers present in your soil or run-off.

happy growing,


Thank-you for your response …I neglected to mention we are using a Hydroponic grow box. Could adding hydrogen peroxide to the water in the correct amount and strength help this situation ? We also have a Blueberry that hasnt shown any visible growth for 2 weeks. We checked the PH of the water and it was around 6.3 We are first time growers and now realize that its best not to grow 2 different strains in the same box. We are using the Cash crop 4.0 from Dealzer.


OK, hydro pH should be about 5.8, so your pH is a little too high. The pH can range, it should be as close to 5.8 but it can range from about as low as 5.4 to as high as 6.2 as long as it doesn’t stay at these far edges of the range for too long.

So yes, the pH could be that main thing causing your problems, Something else to keep in mind, especially with deep water culture hydroponics is the water temperature. In hydroponics in general, the water temperature is very important because the roots need oxygen and water that is too warm, the water can’t hold enough dissolved oxygen, and this too can cause nutrient uptake problems similar to pH problems. Ideally, if at all possible the water temperature in DWC (the type of hydroponics these grow boxes usually use) the water temperature really needs to be below 72F, the ideal temp range is about 68F to not higher than 72*F as the amount of dissolved oxygen will drop dramatically above this temp.

Some hydrogen peroxide might help keep bad pathogens at bay and can increase D.O. levels in the water temporarily, but it would not be good for long term.


I filled out a support ticket PLEASE is anyone could bounce some ideas off, that would be much appreciated.