Same thing happen to me I'm using maxsea grow and it was really healthy at the beginning but I got nute lock or magnesium lock and then my pistils was turning brown and I was using calmag+ nothing happen and my nephew came over and he saw it and said his was like that but he was using a different nutes but none the less his plant's didn't grow so he use calimagic and hygrozyme and that fixed his problem so the next day I went to my local hydro store and bought a microscope and calimagic I already have hygrozyme and when we check the leaves there's a lot bugs so I sprayed them and feed hygrozyme and calimagic and bam next 2 days my plants recovered and now it's flowering with clean white pistils. Check if you have bugs cause russet mites will do that to your plants it'll suck the hell outta your plants and get some calimagic it helps with pistil rot. I read a review at amazon and one of the review said (Every tomato that was growing was getting blossom end rot. Luckily I knew how to treat it, and got it on time thanks to this. A must have for a hydroponic grower) I'm not growing hydroponic I'm growing in soil outdoor. I just pick up a gallon of CaliMagic and 20lbs bucket Maxsea Bloom. Good luck Charles lewis