To be on the safe side and wont hurt a bit try and add some calmag next time you water. If thats not the problem it still wont hurt them a bit and might actually give them a boost. Your ppm might have been a little high for beginning stages of flowering. I would start around 1000 and work your way up. By my fifth week of flowering I boosted my ladies feeding schedule up to almost 2400 ppm, so start low and work your way up. and by no means am i suggesting you go that high, my ladies are fucking pigs and most plants can't take that much. You know now that I look at your pics again I'm guessin you just overfed them a little, burnt tips usually means a tad overfed good luck bro