Volksgarden Rotating Garden Problems

I recently bought a volksgarden and I seem to be having some problems with the plants actually starting to grow. They seem to be stunted or at least severely stressed and I cannot figure out why. I have two strains in there and I wanted to start off small so I only have about 25 plants in it. It can hold up to 80.
 
The plants are Grape God and Blue Dream. I have had a lot of success growing these strains in DWC but so far they are not growing as fast as I would like them to.
 
First of all I am only watering them once every 2 days. They are so small and the Grodan Grow cubes hold so much water I have concluded that they must be overwatered. The leaves are yellow and not the deep green that I would like to see.
 
Those bags you see are mushroom CO2 bags. I still wanna find a way to hang them over the unit. Also the light is 600W MH.
 
What could the problem be? Should I start spacing out my watering even more?
 
The PH is at 6.0
PPM is at 371