How long have they been purple? How old are they? I've had tomato plants turn a bit purple when really young, too. It's especially a problem if your vegetation has grown too fast for the roots to sustain them. If that's the case, it'll level out just fine. Also, when young, the roots in a dwc may not be getting to the nutrients. Organic nutrients aren't necessarily immediately soluble and tend to settle. Stir the mixture occasionally.

This tub. . . did you actually mean 3 gallons or is that a typo?

hi joe.jr317,
i started from seed on july 12, they started getting purple a week ago, now they are about two inches tall, the stems are thick, the roots are not in the solution yet they are relying on the drip emitters, for nutrients. yes i will try stirring the tub and test ph, should i wait and see what happens. or should i change the solution and make it stronger?
yes the tub is bigger but the tub can only take 3 gallons or else the bottom of the baskets would be in the solution. i bought this turnkey type of system from a guy in minnesota,
for 350.00 all it needed were new lightbulbs and one new fan, it fits perfect in my kitchen, i guess i thought that was cheap. it's nice though,
thanks for your advice

I believe that most organic nutrients contain bone meal as a source of phophor. Bone meal is highly insoluble and the phosphor must be made available through bacterial action.
To solve this problem in the short term I suggest to add some soluble phosphor (ie: potassium dihydro-phophate) a teaspoon at the time.
In the long term . . . don't use organics for hydro.

hi greystoke,
the organics i use is technaflora pura vida organics
in the derived section on the label there is no bone meal in it. when i first put nutrients in the tub my ph was 6
two days later was 8.5, so i got it back down to 6 last night, my tap ppm is 170,ph 7.5, so i'm letting 5 gallons sit with an airstone in it,and i think in two more days i'll put new stuff in....?

another ? greystoke if i use organics for tomatos then i won't have to flush my system before i eat it right??just want to mention that yes i am new to hydro

greenbrian,
Organics are not designed for hydro. Organics require bacterial action to make all nutrients available to the plants. That is not what hydro is about. In hydro you present the nutrients in the form that can be absorbed by the plant directly.

And . . . "if i use organics for tomatos then i won't have to flush my system before i eat it" . . not sure if I understand you.