Hey dude 
Up your water temp to 20-21c
16.5is a bit cool
You also probably left them in your propagation tray a little to long
If that's a hps your running then consider getting a metal halide Globe for veg then run the HP's once pre flower stretch is done with.
Hard to tell but they look a little hungry.
Do you have an EC pen or TDS/ppm meter? They are invaluable as is regularly testing your Rez and feed water pH.
DWC can push pH up and lock your plant out so until you have a handle on your environment with a few full grows under your belt you need to be OCD with taking readings.
Umm that's it for now, keep it up and hopefully they rocket off for you soon!

6

Up your water temp to 20-21c
16.5is a bit cool

You also probably left them in your propagation tray a little to long
If that's a hps your running then consider getting a metal halide Globe for veg then run the HP's once pre flower stretch is done with.
Hard to tell but they look a little hungry.
Do you have an EC pen or TDS/ppm meter? They are invaluable as is regularly testing your Rez and feed water pH.
DWC can push pH up and lock your plant out so until you have a handle on your environment with a few full grows under your belt you need to be OCD with taking readings.
Umm that's it for now, keep it up and hopefully they rocket off for you soon!

6