Also, not to really give the other answer shit, but runoff pH doesn't really matter (queue the hate). Yes, it can help you understand certain things, but for your first grow tending to runoff is a worry that you don't need to worry about. A trillion things can affect your runoff, hence why I don't even check it anymore.
3 gallon pots, 1 liter of water is all they should need at this stage. It'll gradually get more and more, but I stick by my initial theory of overwatering.