What are you phing, your water too, after you add the MC ? Bring it down to 6.0-6.2, before you give it to your plants.
And if your pot are light as a feather after 2days, it's time to water-feed them again. You need to use at least 3grams of MC every watering,.
If the runoff is around 7.0ph, you should be giving them water with MC in it at 6.0-6.2ph, until you get good runoff., that will help raise the ph in your soil. Where it needs to be.
I'd also raise your light some, the tops are looking a little to yellow, with it being 12inches away, plus too much light will stress them.
At least thats what I'd do, everyone does things differently. Good luck