Week 7 Leaves Showing Burn or Deficiency

I hesitate to post another 'week 7 my leaves are turning yellow are they ok?' type thread. But after my first run last time I'm experiencing a similar outcome during this week 7. Anybody have some input on these photos in terms of cause and what, if anything, should be done to improve?



Strain: Gelato 33

Environment:
Day
78 deg / 50% RH
1000ppm CO2
2x650w Meijiu bar lights @ 100%

Night
68 deg / 40% RH

Medium:
RDWC with chiller and air stones.
68 deg solution temp.

EC is 0.9 and pH 5.6

pH has progressively dipped over the last week or two from about 6.1 to 5.6 and EC has been brought down from 1.4 to 0.9 as it appeared the plants stopped consuming a lot of nutrients. My assumption is that they switched from eating a lot to not needing much and it's caused some nutrient burn.

You are correct, slight over-feed but you are on top of it.

Your environment seems great. Id back off the nutes and should be good to go.

All my RDWC/DWC grows the pH drops around week 6. Im week 7 as well and its crashing fast from 6.1 to 5.8 over a few days in a 120gal RDWC.

Im around 0.8EC at this point with some low N. High K, high S food.

It makes sense if you think about it. Nutrients lower the pH and if its taking in more water than nutes the pH is going to drop because the nutrients are acidic.