Mephisto Pink Livers #1 (LST)

Welcome back to the Pink Livers! Day 42 - Height: 17" Everything coming along nicely with this plant, the buds are starting to progress nicely into decent flowers now. She seems pretty set and I don't think I'll need to bother too much with training anymore, maybe reel in some stems now and then and a little defoliation. One slightly frustrating thing, she started to show a couple of small brown spots on the leaves, very similar to the problems I've been having with the Creme Brulee grow. This is a pretty big concern, but luckily I seem to have caught it early enough. It still looks like a calcium deficiency to me and fortunately, mid last week I threw some Cal/Mag at 2ml/l into her feed just to buffer the soil a little. It's very weird though, I've never had this problem before and now twice in two grows... Makes me wonder if something has changed with my water supply. I've ordered some de-Ionized water and a PH and TDS test pen so that I can test my soil and double check to make sure things are still okay there. If anyone has any clue as to what the rust spots are, do let me know in comments, cheers!