it's definitely not a pH problem. Your ppm measurements are fine. If the edge of your leaves are brown/burnt and curled up, then it's excessive light/heat. But I don't see that in your pics, which makes be believe it's something else. How far is the light from the top of your plants? Check with the company that made the LED, but normally it's 18" from the top of the plants during flowering.
Even though it's only affecting the top of the plants, it's more likely that it's a cal-mag deficiency or overfeeding nutrients. You mentioned feeding magnesim, but are you feeding with a cal-mag nutrient? Do you check the ppm of your mixed nutrients in water? There are a lot of blogs on this website that talks about ppm levels during veg through flowering, but the best way to rule in or rule out the notion of overfeeding nutrients is to start with a ppm meter. I had overfed my plants during my last grow, so I'm using a ppm meter during every feed.

Thanks for reply, no, edges and not burnt or curled up. Light is 350mm from top of plants, does need to come up a bit, but max I can take it is another 50mm at most. I read that potassium deficiency can caused plants to stretch a bit, so I think they're taller than they should be.

I'm using ppm meter, reading about 1500ppm, or EC of 3. I know thats quite high, but with the previous deficiencies I thought I needed to bump nutes a bit. Used calmag a few times earlier in flowering, but not recently. I thought overfeeding nutrients was tips and edges burning, not middles of leaves like I have? Shold I try and dial down the A+B and add a little calmag instead?

15 to 30cm from plant?

Custom45 said:

Thanks for reply, no, edges and not burnt or curled up. Light is 350mm from top of plants, does need to come up a bit, but max I can take it is another 50mm at most. I read that potassium deficiency can caused plants to stretch a bit, so I think they're taller than they should be.

I'm using ppm meter, reading about 1500ppm, or EC of 3. I know thats quite high, but with the previous deficiencies I thought I needed to bump nutes a bit. Used calmag a few times earlier in flowering, but not recently. I thought overfeeding nutrients was tips and edges burning, not middles of leaves like I have? Shold I try and dial down the A+B and add a little calmag instead?

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ec 3 in my opinion is way to high . i would be more like at 1.4ec

Shayne010944 said:

ec 3 in my opinion is way to high . i would be more like at 1.4ec

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Thanks. Could this be causing the brown patches on upper leaves? Not showing any other sign of nute burn, like burnt tips etc.

Just mixed up next feed, ec about 2.4.

Also, just been inspecting a few leaves... spotted some spider mite, fuck sake.

What's a good way of exterminating them at week 4/5 flower?

I use a product called plant therapy which is good for getting rid of mites. Very safe- you can use it up to harvest. Neem oil works well, but I like the Plant Therapy product. Don’t be afraid to spray them good for maybe 2 or 3 days. BTW, mites come out when heat is too high so reduce to 24 degree C.
Your ppm is very high which again goes back to my suspicion about excessive nutrients. Try backing off to 2/3 or even half nutrient. Better to under feed instead of over feed. Hope this helps. Best of luck to you.

Cheers, yep I've dialled back nutes and will continue to do so. Mainly the A+B for now, while I'm feeding pk13/14 and a little calmag. I'll keep the lights at 80% for now and see how it goes.

Ordered some predator.miye sachets to hang up and will pick up spray later today. I'll.lost back in a week or so with an update. Thanks again.

Custom45 said:

Hi all,
Growing a few plants in coco coir, feeding Canna nutes (in week 4.. feeding per 10 litre: 45ml A+B, 25ml Cannazyme, 15ml pk 13/14, 40ml Boost accel, and adding a little TNC Bactorr s13). Temps with lights on 25°c, lights off 20°c. Humidity around 45-55%. Had some browning on leaves and wanted a second opinion on cause. I think it may be light burn.

I'm feeding every other day, each plant is taking about 3 litres. In week 4 of flowering so using pk 13/14. Previously had what I think was potassium deficiency (brown leaf edges and some yellowing) so I started adding a small amount (.3ml per litre) of pk 13/14 in week 2, that seems to have gone away. Also had what seemed to be either nitrogen or manganese deficiency.. lower leaves were yellowing and turning brown. I've been pHing water to around 6.0-6.2, however I checked run off and it came out around 6.3, I read plants take up manganese at slightly lower pH, so lowered to around 5.6 for last few feeds, that seems to have helped, can't see any more leaves turning yellow.

However I've now noticed the brown patches on some top fan leaves. A couple of leaves at first, then a few more, and now even more. It appears to be spreading. Light is a 300w Lumatek Attis led, approx 350mm from plants. Was at 100%, turned down to 80% but problem still getting worse. Think it's too close to the plants. I can raise it, but only by 50mm or so. Is this a light problem and if so whats best course of action? Lower to 60%? I'm worried buds and leaves on plants edges won't then get enough light.

Another thing, I could be wrong, but I'm sure buds have slowed development since I noticed this.

The brown patches look a little yellow in the pictures, but they are browner in real life....
View attachment 1194468View attachment 1194469

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View attachment 1194472View attachment 1194473

These aren't pollen sacs are they??
View attachment 1194474

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Those pictures reminded me of what my plants looked like in the early 90s where weed was a big nono to grow, you go to the pen for growing then, I took the risk then to know what I need to know now, it was having the lights too low on my plants back then, I learned horticulture from tech school. if you really want to get better at growing takes A LOT OF READING & DETERMINATION, I spent countless nights reading Ed's Rosenthal's books, you can't get better at growing by asking questions to solve your problems, I learned by reading & recognizing an issue & know before it gets too bad

Wonder if my problem is part due to overwatering too? Just realised when I water I keep going til I get run off, if it's quite a bit of run off then I just leave it to soak up/evaporate, but means the base of the fabric pot is sat in standing water for quite a while til that happens.

Been reading that overwatering can cause symptoms similar to what I have. Also getting clawing down of top fan leaves.

I'll go easy on the water and gradually add it in, so I only get small amounts of run off.

That looks like magnesium deficiency. In flower your plants need more magnesium then calcium but cal mag has more cal then mag. I'd give them a teaspoon per gal. of epsom salt once a week.

showing up on top can indicate excess but that being said the underside is very clean with no real read on them. Your first PH seemed rather high to me, but after adjustment you seem to be closer to where you want to be, after dropping your PH whats was the PH of your run off? You could quite possibly be right with the thought that the PH is messing with different nutrient uptake esp cus its not super prevalent it seems the beginning of problem. I dont really think its the beginning of burn the plants look rather healthy. What kind of water are you using? Ye average water tends to have plenty of Ca in it
Wait till a old schooler like @tobh or @Aquaman taps in here for the low down

Thanks for help, really appreciated.

After dropping pH to around 5.6 the run off didn't really change after a few feeds, still around 6.2-6.3

Water is city tap water, however we live in a hardwater area, so it's run through a water softener. However I often forget to top up salt tablets. I check my tap water ec and it's usually around 0.45 before adding nutes.

okay, so i am pretty sure that means your media is a tad acidic. If your putting in 5.6 and getting 6.2 or 3 i would assume your media is close to seven and i believe that your plants want to be closer to six.
What are you growing in? I mean whats your coco mix, buffered..?.. percent perlite? Amendments? Also considering that your on tap with hard water i would say you Ca needs are covered, you prolly want some Mg tho. Franks on the right tip with the epsom salts, lack of Mg can cause uptake problems showing up as deficient in different stuff.

Have you read thru Aquas thread titled How to Water Coco for the best results? if not you should give it a read mate

It may be too late but you really should be feeding the coco cal and mag during all stages when growing in coco. As time goes by your coco breaks down so even buffered coco will start to take cal & mag from nutrients to fill new cation sites that are created as it breaks down.

They talk about it here.

wait a sec....soft water...hmmm

It could it be the SODIUM that your water softener is exchanging your Ca Mg for!!!

ezenzyme said:

wait a sec....soft water...hmmm

It could it be the SODIUM that your water softener is exchanging your Ca Mg for!!!

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Which is exactly what coco does coincidently.

“Understanding Cation Exchange in Coco Coir​

Coco is known as a neutral grow medium, but there are cation exchange sites in coco. These sites on the surface of the coco fibers will form bonds with particular nutrient cations. The cation exchange capacity of coco is unlike soil or other grow media. There are far fewer exchanges and the exchange sites will become stable (buffered) once they attach to Ca or Mg.

The cation exchange sites in coco naturally come loaded with sodium (Na) and potassium (K) cations. However, the sites have a weak hold on the Na and K cations. In the presence of calcium (Ca) or magnesium (Mg), the sites will release their Na or K cations and lock onto the Ca or Mg. Once the cation exchange sites in coco have locked on to Ca or Mg, they are “buffered” and stay stable.

The cation exchange sites in unbuffered coco can pull nearly all the Ca and Mg out of a nutrient solution. If you try to grow cannabis plants in unbuffered coco, they will experience Ca deficiency. This is tough to correct while plants are growing because Cal Mag supplements have a strong impact on electrical conductivity (EC). As a result, the total dose of CalMag that you can provide is limited, even though it all may be going to the coco and none to the plant.

Buffering the coco in advance is a critical step to creating an ideal growing media. However, even in fully and properly buffered coco, you should continue to provide additional Cal Mag supplement.

Why do you need Cal Mag Supplement If the Coco is Buffered?​

The simple answer is that the coco is constantly breaking down. As large fibers of coco break down in the pots they expose new surface areas of the coco fiber. This also exposes new cation exchange sites that will take Ca and Mg from your nutrient solution and reduce the amount available to the plant.

When to use CalMag in Coco​

You should add CalMag supplement to all the irrigation water that you provide to the plant throughout the grow. When adding Cal Mag supplement, you are not adding it for your plants! You are adding it to satisfy the coco. The amount that you need to add reflects the needs of the coco, not the plant.

Coco breaks down due to a variety of factors, but you can expect it to need the most Cal Mag supplement early in the grow. The fresh coco will have the greatest potential to break apart and this is hastened by the roots of growing plants. Young plants spend much of the energy pushing their roots through the coco. As they do so, they contribute to breaking it down and create an ongoing need for additional Ca and Mg to be added. Later in the grow, as plants are flowering, the coco will have become more stable and as a result it will need less Cal Mag supplement. This is helpful, as Bloom Boosters can step in and fill the EC quota that CalMag can surrender.”

So could simply removing the softener solve the problem lol? =P

ezenzyme said:

So could simply removing the softener solve the problem lol? =P

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It wouldn’t change the fact that coco breaks down and pulls the calcium and magnesium to fill the sites.

I run RO (0ppm) and coco. Three years I fought these issues. When I understood why I decided to try it because well what do I have to lose right?

Having the correct nutrient ratio has allowed me to run 3 ec without a sign of nutrient deficiency or toxicity.

I know no one wants to hear cal mag as an answer...but it’s for the coco not your plant.

Day 34
3 ec