What's the discoloration mean?

Give it some oxygen ie oxy plus or hidrogenproxide this will clean and kill any mold or any bad pathergens 1m per lt

Looks like a blight or fungus to me. Septoria? Look it up on google if you wanna look at pix and draw your own comparisons and conclusions. If it is, a copper based powder you can mix in water and spray on the leaves will take care of it. I looked at your diary and you say your humidity is 52% Do you have a good extraction fan? Are you moving the air around with a oscillating fan? Not to step on any toes, but don't spray your plants at lights out. That's a great way to cause a mold problem or allow for pathogen infiltration.

You need extra PK. Also add some Epsom salt as a foliar spray to your plants at lights out. All these are key to stages of growth. You need to up your NPK or as suggested below, (maybe not as I'm gonna say it) but, most of the time. What you need sits in your pot. Nutrients uptake is a key part of growing a good plant. Enzymes or something like a fungi will be so benifical. Feel free to ask on any of these things I've said. If you're interested in it. I'll explain more. Good luck.

give her some more calcium

Hi buddy I had similar symtoms to these when my airpump broke in my old dwc set up are you sure your getting her enough oxygen at the roots ? if its not that my 2nd guess would be either a cal-mag problem or an imbalance in your ph. I would check all that you can run off ect see what you can eliminate. it does not look very serious though and might sort itself out in the next feed I'd keep eye on it buddy :) need anymore help just hit up my dms :)