Tips curling up and browning

I just noticed it on a couple of fan leaves, and I want to correct the problem before it gets any worse. I'm growing in coco, using GH flora series and keeping the pH at 5.5, watering 3 times a week. They are in the 3rd week of flower, and earlier in the veg stage I had to increase the calmag because I kept spotting a calcium deficiency. Could it be related you think?

That's not a calcium deficiency. Coco should be In the 5.8-6.0PH range from what I understand. Adjust your PH.