green slowly fading, sign of major problem or just genetic strain?

I don't know why but my smaller plants (purple monkey balls) have a much darker/healthier looking leaves then the more mature ones. is this just strain genetics or is this a sign that my nutes in the foxfarm soil are running out? Should I be worried? The bigger ones were just transplanted but they've been a light green for a while it seems. some advice would be appreciated.

looks like they need N....u running any nutes since using fox farm?...you should be using nutes like foxfarm or something...i use ionic and love it much cheaper than fox farm.... heres the feeding schedule for fox farm ........................http://foxfarmfertilizer.com/FoxFarm-Soil-Schedule.pdf .........................as you can see during the vegg state the plant needs mostly Nitrogen---i would pick up some nutes...pretty much any brand other than MG....

also it looks like they might be getting pretty close to the final weeks of vegging...the plant wolnt need much N thru flowering so make sure u dont over do it

I have been using advanced nutrients but a couple of Weeks ago, they experience nute burn so I was a little hesitant of giving them nutrients.

another thing to look at is your ph in your water??? any idea what that is

Its a little under 7 , about right.