This is the plant in question 2 weeks ago. this is the plant today: pH'ed the runoff after last watering,- 5.8 ish, but before this it was 6.5. I suspect after next watering, it will go back up, or I will flush it until it does. Have been using plain RO water, and has been fed grow big 3 times, 1/4, 1/3 and 1/2 strength. She wasn't fed until about the 4th week from sprout. this plant as well as my others have experienced some underwatering and heat, being my first grow. Could this be lack of light, the plant is very bushy. possibly root bound? Plant is in day 5 of flowering and she just showed me here privates!
Are all of the fan leaves below the canopy showing symptoms of brown spots as well? It's not lack of light, though your bottom factory blades are going to die off over the course of flowering anyway. She could be rootbound (you can easily check that), but that would not likely be the cause of the necrosis at this stage. 5.8 is low and is a decently big enough change from 6.5. Looks like a pH/lockout problem to me, particularly the last photo. Flush with pH adjusted water next watering and halt the nutes until the browning stops or you hit around 6.5.
That's the plan. I think the ferts have lowered the ph, I gave them three doses, one every other watering. I don't see roots in the drainage holes, but can see the tip of one root just peeking out of the soil at the bottom. It's really only older growth, the real big old fan leaves
Do you know the ppm of your RO water? The one thing with RO water is that, assuming your system is working properly, the ppm will be very low (ideally less than 30) and the pH will be neutral. Anything you add to this water that is acid or base will drastically change the pH b/c the water currently lacks any hydrogen ions (protons). In other words, for water that has little to no ppm, adding fertilizers can easily make the water too acidic for uptake.
I do not have a PPM meter, but it is a 6 stage ro/di system that is brand new. Should I maybe do 1/2 tap, 1/2 RO when I feed? our tap is high ph about 8, and very hard, lime- water report says it varies from 240-360 ppm So you're basically saying it is a pH problem?
Hmm, yeah, I'm putting my money on a pH problem, especially since you were able to accurately measure the runoff at 5.8. Remember a pH imbalance causes nutrient lockout, so the symptoms can depend on what particular nutrient isn't being absorbed. Nutrients are absorbed by cannabis at different pH's, though they are all very close. When a host of nutrients cannot be absorbed (especially calcium and magnesium), the symptoms appear very similar to your third picture. I mix my ultra-high ppm tap with RO water. If there are no documented problems with your tap (there shouldn't be at less than 500 ppm), I think your idea of watering with 1/2 and 1/2 next time is perfect.
ok, so here is a 5-day update, she's looking better, though i had to pull some leaves (only the all dead ones that would come off easily) I don't know if I'm out of the woods yet, but she is looking better after a couple waterings of 1/2 ro 1/2 tap. just ph'ed her today-6.66 what do you guys think? hope my yield won't be too affected, but this is my first grow.
also-I believe this was a ph-induced nitrogen deficiency, or just a plain deficiency. the leaves will go yellow- then the stems turn purple and the leaf can easily be plucked off.
This topic really helped me pinpoint what was wrong with my plant. I have much the same deficiencies as your plants had. Have just adjusted PH of water and hopefully my plant will work out just like yours has!
I am still unsure if it was caused by ph or underfeeding. ph is standing good at 6.6, about to do a light feeding tomorrow. I am hoping to stop this completely soon as she is definitely starting to flower.
