Are you using tap water or Reverse Osmosis water?...It may not seem significant, but the two are different for sure. Have you checked the PH of your soil? You can buy cheap little PH test kits for soil that comes with little capsules or plastic containers that you place the soil sample that you want to test...add the solution that it comes with, shake it up, and match the color it turns to the color chart that it comes with. I grow in hydroponics nowadays, but 6.0 seems a bit low for soil...I know you'd at least want your water going in at 6.5...maybe a soil veteran will come along and offer more insight into soil ph.