Tough to say without knowing the environment and treatment of the plant, but it might be a potassium deficiency.
Is that coco or some soiless mix?
Looks nute locked maybe? Need more Info
As @hoppiefrog said
pH water flush it 2x its pot size
Packee
Start here:
It sometimes is best if you start from scratch. This recipe for soil goes back decades. It was used in the western part of America since the 60’s. The soil preparation for the cannabis plant, depending on variety, is very specific.
The plant is not easy to start or grow to the best quality of flower unless you educate yourself on the necessary inputs and procedures. Good luck 
“IF” the soil in that pot is as new as the plant is, it already has plenty of nutrients in it for the first month of growth. If you are adding “MORE” nutrients to your water, you could burn your plant to death. Flush the pot with about 2 quarts of fresh cool water and keep it in the light for 20 hours a day and watch the new growth. The plant is killing off the bottom leaves for the sake of trying to save the new growth.
Please don’t do anything without knowing what you are growing in. If u happen to b growing in a time released fertilizer like miracle grow or a few others and u flush u will add to the problem. That’s why they are not recommended.
It looks like your ph could b off and your temp and humidity could b out of whack as well. More info would b very helpful.
I’m growing in coco
No I know got a lot to learn
That plant is to Young to flush… way to much water for that her roots are still growing don’t drowned them
I would not of flushed them yet as I thought that it was way to early and was worried I would kill her
Probably ph issues if coco was washed
Coco was not washed
Humidity temps?
@imSICKkid may be able to help u best hes a coco guy .coco needs to be washed if not done previously to sale;)
What coco are you using @kirsh ? If you didnt wash it or rinse it then your ph could be outta whack due to the high salt content in some coco. That plant is definitely old enough to flush but before you do that you should get some runoff numbers. I’m not sure how new you are but if you don’t have a PH and TDS meter then you should grab one. The new growth coming in doesnt seem to be bad looking.
After you check your runoff I would recommend you mix up around 2 gallons of 500ppm water with a ph of 6.0 and you can pour a half gallon at a time, wait 15 to 20 minutes, and pour another half. While your doing that you should be checking the runoff each time in between pours. After the water coming out the bottom matches what your putting in you should be good to go.
@kirsh one could advise to just do a minimum to her for a while. I have a similar plant here that isn’t growing, I just look at her once a week now and she’s doing better. This stage may last for what seems like a while, but if she makes it through she’ll make up for it in the end mon.
Start here with all your questions & issues. Very good website!
We prefer you start her at GN. You’re in the right place. 
Sure. Just trying to help. There’s actually a wealth of information out there if one would take the time to look. Growing cannabis is not like growing tomatoes or beans.