I wouldn't give up yet. Marijuana plants are pretty resilient. Pick up that PH/Moisture meter for $15 from your local hardware or grow shop. If you have a nutrient lock, you can still foiliar spray your plants. If it isn't a nutrient problem your PH is off or you need to tweak your watering schedule. Something as little as over watering can create a lock. Pick up a bottle of organic liquid fox farm or earthjuice. Something with a decent amount of nitrogen and maybe a little bit of phosphorus. The best time to spray your plants is in the morning.