HELP! Help! Leaves tacoing and tips turning black

[Groot]

I have two Grand Daddy Purple plants, in two different tents, two different types of LED lights (600W Viperspectra 20" from plant tops, 300W Electric Sky 25" from plant tops), 9th week of flower, both in a ProMix medium, DynaGro Bloom + Mag Pro nutes in filtered tap water. Both have developed this strange "tacoing" and "black tip" on every leaf including the flowers/buds. The effected stems are under the canopy of large flowers/buds so not in direct light. Otherwise I would have thought the light is too close. However, I don't see anything like this on the large buds that are closer to the lights in the top canopy. First three pictures are the plant under the Viperspectra LED light, the last three are under the Electric Sky. Anyone seen this before?

[oldjarhead100]

Have you done a flush on them ,gives you a chance to check ppm and ph in the runoff, I would say the curl is because you reached the plants max uptake of nutrients and you have the perfect amount of nute burn, turning black is why I say a flush maybe others will know more

[Groot]

Thanks Oldjarhead 100! I did a pseudo flush (i.e., fed until there was run off). A few weeks ago, I had noticed that my run off was low (5.4 pH) , so for my follow on feedings I went high (6.4 pH), it took a few feedings until my run off was 6.2 pH. The last three feedings have been 6.1 pH and I didn't check the run off. Maybe the period of high pH feedings caused this?

[Groot]

Thanks Oldjarhead 100 for your help!

[OlderNOTwiser]

https://www.growweedeasy.com/cannabi...t-light-stress Looks like heat to me.

[oldjarhead100]

it could be but they sound far enough away

[Groot]

Thanks OlderNOTwiser! I keep a running log of my tent temperatures, max temp was 73 F for the plant in first three pictures (also the original problem). Max temp for the other tent/plant was 78 F, heat could have been the problem, but why only one stem and it is a lower stem (not direct light)?

[Groot]

Thanks OlderNOTwiser for your help!

[SoOrbudgal]

Is it to warm, are fans blowing warm air?

[Groot]

Thanks South Oregon Bud Gal! I have one fan blowing over the tops of the plants in the smaller, cooler tent. I have an upper and lower fan in the larger, warmer tent. It definitely feels warmer in the larger tent...and I am measuring temps at floor level (I was concerned that that roots would get too cold)...so it is definitely warmer than what my readings are telling me. I may need to have a different hygrometer/thermometer to find out how "hot" it is at the top.

[Groot]

Thanks SoOrbudgal for your help!

[oldjarhead100]

do you have a exhaust fan that blows air from your tent to an area where it can dissipate and not go right back in the tent

[Groot]

Originally I was anticipating that my garage would get cold during the winter so I rigged the air intake duct (to the tent) to draw air from the ceiling, using the warmer air at the ceiling level. My exhaust fan with filter is close to the intake. Once my lights turn on tonight, I will move my air intake away from the exhaust and much lower than the ceiling. Great advice! Thank you!

[Rwise]

Move that hygrometer/thermometer to canopy level and see what the temp is there.

[Groot]

I moved the hygrometer/thermometer last night and noticed at least a 7 degree increase in temp. My poor plants were cooking, reading the temp at the lower level/floor the temp was 78 F while at canopy level it was probably 85 F or more. So I definitely had a heat problem but didn't pick up on it in time. I saw the tacoing (heat stress) but the black tips were throwing me off. Also, and I guess thankfully, it only seemed to have an effect on the lowest stem/branch.

[Groot]

Thank you Rwise!