Yellowing leaves, brown spots, tips pointing down and are brittle and burnt,

So I just popped in here again as I saw there had been another answer and wanted to know what someone else's take on your problems was .... and it was you! Just a head's up - this page isn't, unfortunately, like a chat room - no one is notified even if you tag them... But if you've been feeding them, then what you most likely have is a lockout - caused, most likely, by the PowderFeeding which has an enormous amount of nitrogen in it... plants, in flower, don't need as much nitrogen and so that particular nute is often cut down to the bare minimum during flower.... to continue to give it leads to a toxicity which prevents the plant from uptaking the other nutrients it needs - like calcium and magnesium... I'm thinking you need to flush your plant out (3x the pot volume of pH'd water so since you're growing in a 16L pot, that means 48L of pH'd water through each pot)... at the tail end of the flush, give them 1/2 strength calmag and PK and cut your PowderFeed to 1/4 of whatever you were giving... then let them dry out before giving them a watering. When you start feeding them again, you can take the calmag and PK back up to whatever (you might want to increase your PK because this is what the plant is really crying out for) but don't go above 1/2 strength on the PowderFeed... and even that much PowderFeed might be too much... I'm totally unfamiliar with your nutes but I would think they'd have something for flowering? In any event, the amount of nitrogen given at this point needs to be drastically reduced... And if you want to chat with me or another grower, there's a paper airplane in the bottom right-hand corner of the screen - click on it to go to the chat area and search for a grower... and if that little airplane is ever green, it means someone has sent you a message! Good luck..