Ok here is what sometimes happens. Water and nutes are allowed to dry on your media. Once the water has evaporated the nutes are left on your grow media each time you water there after some of these excess nutes become once again soluable and available to the plants roots. This excess causes slow growth, twisted leaves, and deformed plants. I know you said this is your 2nd grow are these the same hydroton balls you used for your first grow? If so how did you rinse them?

PH for max hydro yield is 5.8 - 6.5 or so. Dissolved solids in PPM for seedling stage is 450 - 600 PPM, for Vegg is 600 - 1000, and for flowering 900 - 1400. These figures will give you close to maximum growth with most varieties. I would also recommend the Jorge book it is excellent.

Herbus