I've been growing hydro for about 2 years now and I can tell you that all you really need is water for that baby right now. I have never had to use anything for the seedlings until they start to show their 3rd set of leaves. Even when I move them to my waterfarms, I still use water for them until that third set of leaves comes in and then I start off with seedling stage feed. But yes it could be the superthrive that would be affecting your plants growth since its so small. your ph won't harm your plant so much as long as you keep it between 5.5 and 6.5. A reading of 6 is ideal but I have had it bounce like that before and finally settled at around 6. Good luck... hope this helps. :jointsmile: