Leaf Tips Turning Brown at Day 32 of 12/12

For about a week I've noticed the tips of some leaves are turning brown. At first I thought some leaves were showing a slight mag deficiency, so I foliared a weak epsom solution. The leaf-tip browning continued to progress so I thought nute burn. I lowered EC from 1.8 to 1.4. Now several days later, the "burn" still seems to be progressing.

I've been feeding at an EC of 1.8 since before flip and the plants seemed happy. I thought that at day 32 of flower they shouldn't be wanting less nutes.

Growing in coco/perlite. Hand watering daily with 10-20% run-off, now at EC 1.4.
Temps steady at 77. Humidity 70%.
LEDs are CXB3590's at 1400ma - 12" above canopy.
Good air circulation/ventilation.

NPK at the moment is 1-1-2
PPMs - 126-64-240-159-71 (diluted to EC 1.4 with RO)

what's with all the ppm values? 1.4 is probably too high. looks like over feeding in your photos.

polishpollack said:

what's with all the ppm values? 1.4 is probably too high. looks like over feeding in your photos.

Click to expand...

Thanks. PPMs are N-P-K-Ca-Mg

It does look like nute burn to me, except that I've been feeding between 1.7 - 1.8 for the past 4-5 weeks and they were happy with that. Now even at a lowered 1.4, the burn is progressing. Perhaps with the slow transition to a 1-1-2 ratio, they require a lower EC. Maybe I should go to 1.0 - 1.2?

the green color looks rather light, as if nitrogen isn't the problem. If you had too much nitrogen, you'd probably see dark green leaves. if the color is true to life, then maybe they're getting too much of something else. just don't know. kind of looks like they're being poisoned with too much fert, but since I've never seen light green with dying tips before, it's hard to say. good chance that the coco has held onto nutrients, so maybe you don't need to feed often. it's just hard to say and can't help you much.