Discoloration and brown spots

It definitely looks to be the start of a calcium deficiency but the question is why - until you know WHY, you can't do anything about it. Calcium deficiency comes from a couple of different causes: Nitrogen toxicity or a pH that is badly out of range. If the diary you have is this particular grow, and the pH has been maintained at 6.2, that's not your problem (and you need to update your diary!).... In the last week of your diary, you reported quite a heavy feed of BioGrow so my suspicion is that you've got a nitrogen toxicity which is locking out the absorbtion of calcium (calcium is definitely present in sufficient amounts in your nutes but the plant can't get at it because of the toxicity). I would suggest you need to do a flush here and get rid of the excess nutes... 3x the volume of the pot with water pH'd to 6.2.... let it dry and when you go to feed again, do so with only 1/2 strength nutes. You can add some calmag to that as well. Going forward after the first feed, you should probably monitor your EC or PPM rather than just the feed chart of your nutes. Good luck!