Well dont use cold water, prob the first problem, and dont water log the plants, this looks like a sure sign of root rot, pick up your pots before watering every 3-4 days allow not just the top of the soil to be dry but the bottem as well if your roots are always sitting in water they will rot and not be able to absord nutrients. Is this reused potting soil? What brand? Have you tested PH of your water, and also ph runoff, it looks like your ph is way off and blocking out N and maybe P or K. Also looks like your using milk jugs for pots, really a poor choice for 1 the light will penetrate the sides and mess with the roots, try putting something around them to block out light. Twoo they better have big holes in the bottem to let water run off if it just sits at the bottem we are right back at what i was saying before root rot.