Sick Plant Just started Dwc

? They are not weight lifters! 68 degrees for RO water temp.. ambient temp 75 degrees.. ec 300-350ppm/700 Ph 6.2-6.1 at max!  (Less is more)

Give them a little sprinkle of Epson Salt (Mag / Sulfer) boost. It will green up everything.. a little calmag too!

I'm thinking it is potassium deficiency in my opinion but will hopefully get an accurate diagnosis from u guys

@austin15 but too young for a potassium Def really mate. The pH should be between 5.8 and 6.2, so you're a little out of range. Fix that up and you should be looking better in a couple of days.

@Austin15, like Macky said lower your PH to 6.0. Lower your EC to .6. Make sure you have Cal/mag in with your mix @ about .3 EC. If you put a cover over the top of your net pots light won't get in and cause root rot. Start using hydroguard or another beneficial bacteria if your not already. You've got a good start, keep asking questions and it will happen.  Good luck man.

Awsome everyone thankyou for the awsome advice I will do sll the above 

you're early and not looking bad. I'd suggest getting yourself a copy of Marijuana Garden Saver. You'll learn a lot, answer simple questions and help identify deficiencies. Remember free advice is worth what you pay for it

Looks like the lads have jumped in already with the sound advice, I am going to jump on that PH train, 6.4 is high for DWC, too high or too low will create a lockout situation where the nutrients are not available for the plant, at 6.4 quite a few nutrients begin to fall off being available for uptake and will show as deficiency's ( this is the most common cause of issues and we have all done it at one stage so don't stress) thankfully its early days and you have the percy crew to help right the ship. Get that Ph down and lower the ec a touch as woodi suggested, I would also keep an eye on the water temps in the reservoir, things can get hot real quick in those things and if your not already running a chiller i would suggest looking at ways to effectively keep that water cool. Other than that Good luck !!!!