I have some jems i been growing at all differnt stages but every time i get a jem into the 2nd week of flowering my plant will yellow up the big fan leaves than turn brownish and purplish and fall off. i currently have Advanced nutrients Micro,grow,bloom,b-52,voodoo juice, and big bud. and calmag by technoflora. i boosted the potassium up to half strength and introduced calmag quarter strength and it didnt seem to help. i feeed water between every nute feedings and my ph is on point i calibrate and test frequently. so not sure if maybe my base nutes are reaching there shelf life. i called Advanced and they say they have 3 year shelf life. ive had them for a year and a half and who knows how long they were at the grow store sitting. im not 100% because the plants like the nutes during veg. otherwise the product in the end is still to my liking even with these problems i just dont know what im missing. i will be switching to roots excelerator instead of using voodoo as soon as im out of it. 
