Browning leaves in week 6 of flower

[bongoman]

Hi there

My plants are at week 6.5 since I sexed the females. One of the three is doing fine, but the other 2 are showing signs of deficiency on the older growth. Note that these two seem to be a different phenotype in that they are smaller than the third.

See images for the type of problem - leaves are browning off and drying out. Here's my form:

Strain of Mj? Guerilla Gold
Hydroponic or soil? Coco (canna, no perlite)
From seed or clone? seed
Age of plant in question? 6.5 weeks into flower
What stage (Veg/Flower; how many days into)? 6.5 weeks since first pistils
Medium (Soil, Rockwool, Hydroton etc.)? coco
Container/Pot size? 3 litre
Water runoff Ph? N/A for coco
Nutrients added? Canna Coco A & B & Monsta Bud
Feeding schedule? every second day
When were they last fed/watered? 24 hours
How are you determining when to feed/water (weight, wilting, etc.)? every 1-2 days regardless of weight
TDS/EC/PPM? not measuring
Tap/RO/Distilled water? tap water
Ph before and after adding nutrients? water pre nutes = 7.8; after = 6
Is your Ph equipment properly calibrated? overdue for calibration
Light intensity/Age of bulb/Wattage? sunlight - 7 hours direct a day
Relative humidity? 70-80%
Growing technique (Scrog, Sog, Supercropping etc.)? single cola plants, no topping or LST
Has plant recently been pruned, clones taken, fimmed or pinched? No
Pests? some thrips, manually removed when spotted

Any clues appreciated.

 

[dbfr3sh]

and the pictures are?

 

[bongoman]

Just added the pics - hope that helps.

 

[Cruzin]

Is your humidity actually 70%+, if so you are about to have some rotten shit. Your PH is too high for COCO. It should be like 5.6. It also looks like the issue at hand is a big calmag problem.

 

[Weedhound]

Yes drop the humidity for sure. I don't grow in coco so can't help you there but get the RH down at LEAST into the 40's if not lower. That's the only advice I can offer and I realize you need to do more than that but....again......coco.

I'm sure a coco expert can help you with rest. I can only speak about your RH; but at 70% it's way too high.

 

[Weedhound]

Is the ph for coco 5.6? I thought it was higher, but I am not positive at all.....coco..... I do know that is the correct ph for hydro......not at all sure that's righ for coco.

good luck.

 

[bongoman]

Well, it's outdoors so I can't control humidity, late summer in the subtropics. No sign of mold at all and am inspecting daily.

Humidity the last few days has been down but still peaks at around 55-60%.

As for ph of 6 being too high for coco, I was under the impression that a ph range of 5.8 to 6.3 was ideal and that's what I've been aiming for. Coco is higher than hydro.

So calmag deficiency huh? I thought it might have been that, growing in coco and all that. Thanks for the help. Off to get some calmag then.

 

[chubbynugs]

Yeah flush with a nice mix of nutes with calmag and you should be straight. They look like the cal mag def is also locking out other nutes.