It's been 12 days since your last watering. Have you gone through ledrf thread? If it was me, growing the size of plant you have I would water once daily since your in coco with 1/4 strength grow nutes and calmag. Get a little run off. Do it for a week and see if anything changes
I hope you don't mind me reposting this #2 is what I see
The is a quote from ledrf.
1. Coco holds 30% oxygen when fully saturated.
2. If you let coco dry out, you will get lower yields and most likely nutrient issues because when the coco dries out, it leaves dry spots, where the roots dry up and die. That causes issues.
3. When you water every day or twice a day or ever three times a day, you are replacing all the oxygen the plant used up, thus letting it grow faster. You are also replacing any nutrients the plant used up with fresh nutrients. This is why I water every day with nutrients.
4. You get hydroponic results. Fast growth. Bigger yields.