The pH of your soil run-off needs to be 6.5-6.8. Your running too hot, you need to get that soil pH up to at least 6.5. Your currently starting to see the effects of your soil pH being too low.

Not sure if you know the way to get that number dialed in so here is a quick explanation.

First you want to test your tap water, so for this lets say that is 7.5 before adding nutes. Now you want to run some water thru your medium and catch some of the water as it runs out. Testing that will tell you where your soil pH is. Adjust the water that has NOT been added to the medium to get the medium pH where you want it. Run that water thru, when your run-off water is at the right pH then you can add nutes to your water and then water your plants with the nute water. You should see an improvement within 24 hours if done correctly.

Secondly, dont feed your plants nutes yet, you shouldnt use nutes until the plant tells you or you have seen about the 5th internode (thats how i judge anyways) and then start with 1/4 strength nutes.

Hope that helps.