Cinderella 99 leaves are turning brown and curling. The stems are also appearing purple

As you can tell from my obscure name, I’m growing both Cinderella 99 and OG kush. I got my seeds from a reliable online source but this is my first time with hydroponics. I’ve read things saying that my issue could be a calcium deficiency and the best ph level to consume calcium is 6.2 so I flushed the system and one week later, I’m currently having the same problem. I saw a few other things but I’m not getting a straight answer on what it could be. I am new to this so any kind of feedback is well appreciated! One of the Cindy 99 plants is having this problem but the other one showed early signs, then practically stopped. The pictures are of four plants, the front left is the one that is struggling. The back left is the second Cindy 99 and the other two are my OG kush plants (which seem to be thriving just fine). Thank you again for any advice y’all have. Have a good day!
P.S they are all getting the same nutrients provided by flora bloom