Bottom leaves, tips seem "burnt" - what causes this?

I've been following the http://cocoforcannabis.com instructions to a tee, currently:

1. Strain: Jean Guy photo
2. Age: ~16 days past cotyledons
3. Medium: Coco, buffered w/calmag (per Dr. Coco's instructions)
4. Humidity 75%-80% stable
5. Temp: 23-24C stable
6. Light: Migro 100, 22k LUX measured at canopy
7. EC runoff is at 900
8. Have potted up about 1 day ago
9. Water pH runs between 6.1 and 6.2

I am using the Advanced Nutrients mix of Grow/Micro/Bloom along with B-52 and Voodoo Juice. Clean mix is 1600 EC, so 900 EC is about half strength (been ramping it up slowly day to day per cocoforcannabis instructions).

First pic, is a shot from just yesterday:


This next shot is from just now, bottom leaf tips are looking kind of "burnt".

Any ideas on what might be causing something like this?


Thank you for your help!

You mean 900 ppm which would be 1.8 EC don't you? And a plant that size doesn't need nutrients that strong.

I hope I haven't screwed that up! I am using the bluelab ppm pen, which has an EC setting (it also has PPM 500 and PPM 700). From what I'd read, EC with this device was truly just that; EC (https://www.planetnatural.com/wp-content/uploads/2014/12/ppm-pen.pdf). (0.9 EC)

My guiding reference was here (https://www.cocoforcannabis.com/how-to-grow-cannabis-seedlings-in-coco-coir/#preflush) where he writes:

> the container until the run-off is less than EC 100 (0.1)

I assumed that 0.9 on the pen, meant 900 EC.

I've gotten some tips that this might be related to VPD. I'll try working on that.

So I had one night with better VPD, temps were 26-27, and it was sitting around 72 degrees F.

Unfortunately, it looks as though this "tip" problem is starting on the leaves at the second node as well.

What ailment does this? Starts on the lower leaves, works its way up, and crisps up the leaf tips?

Advice appreciated, this poor girl needs help.