HELP! Leaf tips browning after switch to 12/12

[bumblepuppy]

Hello fellow weed fans. I would very much appreciate some advice from more experienced growers in rectifying my problem of leaf tip browning. I am growing two indica-dominant plants in coco coir using Terra Aquatica Tri-Part nutrients (as I understand, the European equivalent of General Hydorponics Flora Series). My light source is a Mars-Hydro Pro II Epistar 320 LED.
Up until the switch to 12/12 neither plant had a single blemish. The switch to the flower phase meant a modification to the nutrient quantities and I suspect this is where the problem arose. TA does not provide much more than basic info on either their labels or on their site but, forwarned by advice given in GWE tutorials, I have been halving the amount of nutrients recommended from day 1 right through veg. and up to the present fifth week of flower.
My pH is always within range, both going in and draining out. I am putting enough nutrient water into the pots to allow a significant run-off for flushing out any build up of salts. I water every second day.
I have been measuring ppm in and out, but the science confuses me so am not sure how to respond to the results. But, with last watering, the ppm going in (both plants give roughly similar results) was 630 and the run-off, 582. TA recommends an EC - given in millisiemens - for the entire flower phase of 900 to 1000 ppm (I took the ppm equivalents from another site). My measurements, being lower, would suggest that nutrient burn is not the problem (?). I mix the nutrients into tap water that measures around 243 ppm.
The leaf tip browning affects both the leaves at the top of the canopy as well as the under-story where they are shaded somewhat from light -- so I do not think light burn is a possible cause. The LED generates a fair bit of heat but I am using a portable air conditioner to keep the temp. to around 22 degrees Celcius. The lamp is positioned at its maximum height for 'flower' as recommended by the manufacturer (18 inches).
The browning seems to be confined to the tips of leaves while the edges and middle of leaves are, so far, unaffected.
Should I perhaps increase nutrient quantities, I wonder? If anyone is familiar with the TA Tri-Part Series, I am currently using 0.8mls per litre Micro; 0.4mls per litre Grow and 1.2ml per litre Bloom which is one half the recommended dosage.
I would be hugely thankful to anyone who can identify exactly what is happening here. Please see my pics.
Thank you to all who respond.

[Bluey]

I grow sativas and would be giving an EC closer to 1400 plus existing tap so about 1600 at that stage.

Browning of tips is normally nute burn but it doesn't look like it. You also have yellowing of the margins.

I'd be inclined to up the EC and also the frequency. I wouldn't run off every water, just once or twice a week at most. You can do a whole grow without salt issues and mostly zero runoff and perhaps a flush at midway.

https://www.growweedeasy.com/cannabi...ium-deficiency

I think it is the above, a potassium deficiency. What pH is going in and is it a good pH meter properly calibrated?

[9fingerleafs]

Right on the money. Should be giving full dose of nutrients at this point. Most people even use bloom boosters in the 3 to 6 week. Also the runoff thing, the EC inside the medium (run off) should be 3 to 4 EC = 1500 to 2000 ppms. You should be watering at around 1000ppm. And let it build up little by little right up to week 7or8 when you stop the feeding. Also check pH

[SoOrbudgal]

Hello and welcome to the forum. I do not use your brand of Nutrients but it looks like high N effecting the leaf. How many plants, are they autos or photoperiod ? I do see that you'd help the heat an air flow in the tent if you removed just a few leaf off each plant especially near the bottom. And are you letting them dry between waterings/feedings? Lower the N during flowering helps also.

[bumblepuppy]

Hi guys. Thanks for taking the time to offer your advice.
To answer a few of those questions: I have two plants, both indica dominant, feminised, photoperiod. I have removed some of the lower leaves of each and have two fans positioned to blow upwards into the foliage. My nutrient pH going into the pots is between 6.4 and 6.8 (for flower) measured with an HM Digital PH-80, calibrated to pH 7. Runoff is never more than a couple of pH points one way or the other.
Regarding runoff, I have been led to believe, maybe mistakenly, that a 20% runoff with each watering is mandatory to eliminate excess salts, a condition that impedes the roots taking up water? Apparently this is not a hard and fast rule.
But do I act on the possibility of Nitrogen excess or increase nutrients - thereby raising ppms - and hope that this will resolve a K deficiency? Today is watering day so I will cautiously act on the latter for a while to see what happens. If the problem persists, I'll consider the Nitrogen issue.

[Bluey]

You need to drop your pH. That explains the Potassium deficiency. Bring it down to 6.2 and keep it 6.1 to 6.3, no higher. pH at the roots will be close enough to 6.5 which is your target in coco.

Running off every watering makes it more difficult for a max yield harvest. Water more often and take note where runoff occurs and reduce the amount your flushing down the drain. Water more frequently and don't let the coco dry out apart from the top little bit from time to time.

As 9fingerleafs & I have said bring your EC up to about 1.6 and continue bringing it up to a bit above 2.0. 1.6 to 2.3 max works well for most plants and it does vary a lot depending on lighting environment plant size and strain.

[bumblepuppy]

pics from today . . .

[Bluey]

Get your pH down and half your problem will be fixed immediately

[Rootsruler]

Yer pH is not the real issue here. You are slightly out of range but that shouldn't affect your plant like that. I'd shoot for 5.8 - 6.3

Looks like you're in week 4 -5? Looks like you're running a blurple? LED's tend to increase magnesium needs. Coco also tends to not to like to hold onto mag. Between the LED, Coco and half strength feedings you're lacking in mag is my guess. One teaspoon of epsom salts for every 5 litres of water.

[bumblepuppy]

Well, the Terra Aquatica recommended pH range for the flowering phase is 6.4 to 6.8. I understand that an in-going target should be at different points within that range for each watering. The run-off is usually only a point or two either side of water going into pots so I figure the average is usually within range?

[alltatup]

I'd recommend a 24 hour flush each week before you change nutrients--and lower nutes a bit.

[bumblepuppy]

So, LOWER nutrients rather than increase? I used 1/2 strength nutrients all the way through veg. and into first few weeks of flower. It was only at the switch that the leaf-tip browning started to occur. Now, I've just started gradually upping the nutrients according to other advice.
I was planning on using Terra Aquatica FlashKleen and then FinalPart-Finish for two weeks before harvest. Both Train Wreck and Blueberry take about 8 to 9-10 weeks in flower. Its just about week 6 at this stage.

[alltatup]

bumblepuppy https://www.growweedeasy.com/?s=nutrients
My experience is that most feeding schedules are higher than they need to be: I adjust according to the number of plants I'm growing and I'm usually quite below what they recommend, but my leaves are dark green. Each grower has to find the perfect spot.
By the time we switch to flower, if you haven't been flushing regularly, the plants often display signs of needing a flush, or less nute. https://www.growweedeasy.com/flushing-sick-cannabis

[Rootsruler]

If TA is recommending those pH levels then I would stick with those for now unless you want to experiment to see at what pH the plants respond best. Almost always I find that "deficiencies" are not the cause of the problem so much as an imbalance causing lockout or decreased uptake.



I like to use this chart as a guideline for the basic need of the plant and the timing of nutrient ratios.



One other thing it might be is you say it's at week 6. This is usually where you start to see leaf senescence meaning you're approaching the beginning of the end depending on genetic makeup.

[bumblepuppy]

I've been experimenting by varying the pH despite the TA recommendation. But any adjustment takes time to show results. So far, there has been no change. (It's frustrating that just about every weed growing website gives differing advice).
I started the grow at half the recommended nutrient dosage according to the advice as I understood it from GWE tutorials. After the switch to 12/12, that's when the problem started. Now I've increased the nutrient to 85 percent of the recommended dose. In two or three weeks it will be time to harvest.

[Rootsruler]

PLEASE......NEVER flush a plant in soil unless you are experiencing a heavy toxicity issue. Flushing will stunt your plant and extend your grow time. Better to do clearwater feeds with runoffs to dissipate whatever overabundance may be in the soil and let the soil sort out the rest.

[bumblepuppy]

I don't know who that caution was directed to. I'm growing in coco.