First...Welcome to the wonderful world of Hydro. I have about 3 years experience doing DWC.
1. Not sure if you expected this, but your plants will nearly always go through a mild shock when going from soil to hydro. They appear to be at least a few weeks old, and the older they are the harder the shock will be. When doing this, let them be in straight water for a few days pH'd to your hydro standard. You appeared to have given them nutrients during the first three days...that's a no-no. I mean, the plants are stressed out from the shock, giving them nutrients won't help and can only hurt (at least for the first few days). Once they're feeling better about their transfer, I would reintroduce the nutes at half strength (300ppm) for the first few days. Then go up to full strength.
2. Get a real hydroponic pH, TDS, and Temperature meter. Toss that stupid vial away. There's reasons why people grow in soil...one of the big ones, it's more forgiving (meaning hydro isn't). You're 100% responsible for the plant's environment all of the time and the plant reacts in a much more volatile way to unfavorable conditions. Once you get a meter, keep your pH around your sweet spot (5.5-6.0) depending on the strain...For plants that young, I'd keep the TDS around 600ppm. Your water temp needs to be about 10F lower than the room temp in an ideal situation. Make sure you're pumping lots of oxygen into your water...it's hard to measure, but go no the side of caution...cuz you can't over oxygenate your water.