Multiple issues (purple & yellow leaves, brown/purple tips)

[Ergot]

Greetings GWE braintrust!

This is my first proper grow (the others have been plant and forget outside) so this is still a learning curve for myself. The plant is an auto northern lights grown under an advanced platinum P300 LED, 18" away, end of week 6 from germination temps 19.5C - 25C and humidity 41% - 55%. The plants have been fed using the Nebula's auto schedule for GH. Out of the three plants, this one has been troublesome since week 3, the others are growing without issues.

The newest leaves around the main colas are becoming discoloured, a deep purple colour, starting at the tips of the leaves and moving towards the centre along with the leaf turning yellow and the veins staying green. Flash on / flash off :



The others that are slightly lower than the canopy height do not show the symptoms to the same degree, just yellowing leaves and purple/brown tips so presumably will start discolouring more in the next few days. Is this a molybdenum deficiency? Although the ph levels are well within the 5.5 - 6.5 range



Another issue that appears to be starting today is two leaves growing from one cola are becoming discoloured but are a different colour to the ones described above! (oh joy) Perhaps it's just a different stage of yellowing?

(you can also see what I believe to be a potassium deficiency affecting some older growth, described below)

The other issues with this plant have been what I believe to be a potassium deficiency which appeared at the start of week 5 (almost 2 weeks ago) which does not appear to be getting worse at the moment and a phosphorus deficiency at week 3 which has since cleared up. Could my current issue be a knock of effect of these previous deficiencies?

For the watering schedule I've been letting the ph sway between 5.7 and 6.5. All the plants have had the following over the past three weeks:
6.4 in | 5.9 out
6.5 in | 6.1 out
6.3 in | 6 out (flushed for plant with issues)
5.7 in | 6.1 out (watered yesterday)

I'm not convinced my ph pen is entirely accurate (I'm ordering a bluelab tonight) as either the readings from the pen are out or I'm looking at an issue with my growing medium and it affecting the ph range, canna coco coir and perlite. Is it normal for the ph range to take a couple of watering when going towards the other end of the scale?

Apologies for the many questions, I'm really stumped as to what the issue(s) are as the ph appears to be in the correct range.

Thanks for any help

[Canuck147]

I agree your ph is okay. You answered your own question - I believe it is a potassium deficiency. Get CaliMagic by general hydroponics or something equivalent and use the recommended dosage every watering. I say this because your plants should be a deeper green.
Don't sweat the purpling, might just be the strain of the plant.

[NebulaHaze]

I agree the pH seems just fine from your numbers. You mentioned that the plant with the symptoms is taller than the others? Is it possible it might be more sensitive to the light? LEDs are really powerful, and I feel like auto-flowers in general can be more sensitive to light burn sometimes (they originated from Siberia in a very cold climate with relatively low levels of light). If you suspect it's the LED, perhaps moving the symptomatic plant to the edge, or raising the LED grow light up a few inches, might be all it needs! Yours is at 18" away, which is far enough for many LEDs, but it's possible that with these particular plants they need a little extra distance

[oldjarhead100]

sounds like you are all set but I would add this ,MY grow room is in the cellar and I have temp. fluctuations of 20 to 30 degrees it often gives the plants colored leaves doesn't seem to affect it in any harmful way

[Ergot]

Thanks a lot for the responses.

Canuck, I've been following the set schedule for calimagic on Nebula's schedule which is what's perplexed me as to why this plant is showing the deficiency, guess I'll have to chalk it up to plant genetics

Nebula, thanks for the suggestion, I've swapped the plant with the problems from the middle to the end, only problem is space is at a premium and I've done my LST for the positions they were in originally doh!

Jarhead, interesting comment I wasn't aware that was a sign of temp fluctuations, I'll definitely keep that in mind, thanks. Do you believe that the higher temps affect the quality of your buds? Only wondering as the site says 26C as an ideal max for flowering

[OzBud]

any higher and terpenes can evaporate from your buds potentially reducing smell, taste and potency