Alrgt Ken............. re gnats, could be of help to hang a few "Diptera" traps up. Dipterous two wing flies are a sucker for the fly trap, the sticky one you pull out from the little cardboard cylinder, pulls out to about 80cm long........just hang 4-5 those up at different heights and take out the adults.......
They are looking bang on Ken.............., with fems is a good time to switch post 35 days, so @42 switch, you are looking at a good bit of stretch still to come, around another 60-90cm, before mid flowering slows the stretch to zero......... should be a nice size last 5wks of flower Ken........ you will like the aroma from them when they fire pistills.
Within a week of 12/12, watch the 2-3-4th internode, with a strong small magnifying glass, and you will see the pre-sex organelles develop. All pistilate calyxes "Sit Down" tight in the "V" next to the "Stipule". Staminate (male) Pre-Sex organelles "Are On A Tiny Stalk" not sat down in tight to the bract etc......... the event in my experience takes place from day 45-65, if it aint happened by 65, you should be ok Ken..........the OHS like the Pk boost from beginning of the last 4-5 weeks, before the 10 day pure water flush begins. i run the Pk @ 200ppm, if my pre nute ppm is 550ppm, i swap out 200ppm of nute for Pk13/14......... 1ml of silicone from the start till end Ken....
The last 3 weeks of flower add boost accelerator if you use canna, or a boost from your nute group etc........ during this period, add with boost, molasses 2tsp in 5ltrs warm water Ph'ed at 6.6 (Flower), feed separate boost inc molasses, every 3rd feed last 3 weeks, will lift flower volume....... AM