Plant turning to flowering stage with 16/8 light scheme

Hi guys,

My 2nd grow, using kratky method with generic nutrients (I know, I know, I cant get the proper nutrients right now, and the oxygen pump is taking forever to arrive due to the Coronavirus)
Light: Chinese QB 120W, running at 70W pulling at outlet. 16 on, 8 off
Nutes: Generic, uncalibrated (pH meter is on its way ) 600-800ppm
Started Vegging 4 weeks ago
Grow strong the first few weeks then stunted, with yellow leaf at the lowest layer

What I dont understand is, how can the seed switch to flowering with 16/8 lighting? (same with my first grow)

Most photo periods plants will pre-flower around 4-5 weeks old. Just pistils right? Pics? Probably nitrogen deficiency but I will need to see pics to be sure

here you are

she definitely is hungry. She needs nitrogen asap.

And those are just pre-flower. Once you get air to the roots and the ph right, she will probably pull thru. Do not flower her for at least 3-4 weeks after you get her back right. The damaged leafs will not recover. Watch her new growth to make sure she is getting better