white widow x big bud scrog 2400w

hi guys, this is my 3rd grow and my first grow journal, which i would like to share with you all.i hope evryone enjoys the show, any feedback or advice would be welcomed.

Right now i am on day 22 from seed but i have been taking pictures daily from start.
i have 4 varieties in total(and like a complete t*t, i have messed the labeling up so i dont know who is who. but i do recognize 6 as wwxbb as i have grown these before and recognize them)

3 iced grapefruit (femaleseeds)
2 superskunk (cant remember)
1 x18 pure pakistani
6 wwxbb (femaleseeds)

set up

-2.4 x2.4 grow tent
-4 x 600w hid`s (only using 2 now)(saving 2 for start of flowering)
-inputfan
-output fan with scrubber
-medium is a 60:40 mix of clay pebbles and vermiculite ( has worked well for me before)
-air pump
-ecotechnics temp/humidity control system( its awesome)
- water pump
- 90l nutrient bin
-G.E.T full nutrient line

here some pictures guys.

some more pics

one of the plants is sick, this has happened to me before the plant will cary on growing till its 2-3 week of flower then it`ll fall over and the stem will be all dry where it snapped from. does anyone know what could be causing this?