Sensi skunk fem

Sensi skunk! Fem not auto! Few other bcn critical fem seeds planted around 3 weeks after the sensi seeds! Any signs that they actually female? First time growing! Some have been topped and lst tried! Also removed a few fan leafs from the bottom! Feeding every two days one hour after lights come on! Main 3 big plants are about 42 days old since germination so I put them into flowering 8 days ago! Not sure if it was too early! When lights go of I have a oil heater that keeps the temperature at the same level 25-29 degrees is this correct? I’m currently using canna coco a and b nutrients with cal mag my mix is 40 ml of canna a 40ml canna b 40ml cal mag mixed in to tap water 10 litres! I’ve feed them this mix since they were two weeks old! Recently feeding 1.8 litres every other day as stated above! Should I be adding flower nutes now? Up the feeding level? Few leafs look like there getting a few brown spots! Do I need to increase cal mag help needed as come this far and don’t wanna mess things up as cost me a fortune so far cheers