A couple of answers of what I do:
1. Top anytime after 3 nodes (but your 6 look great, very tight, just a little taller plant)(I also clone at 3 nodes)
2. I rotate feeding nutes. Sump starts abt 1000 ppm, water and top up w/pure until 200 ppm, then re-mix and start again abt 1000 ppm.
Salt build up and flush time reduced.
However, many feeding routines work well. Somewhat strain specific, somewhat generalized...good luck experimenting.
Ps. PH each and every watering just before watering. A million things can change PH. Blue lab meters are great (the ones you can leave the probes in the water). Beware of 'pens'. Anything you take out of the water WILL eventually dry out......and you get to buy another!
PPs. To solve your fan problem, remove the outer material pre-filter and put it inside the filter to trap incoming dirt before it gets to and clogs the carbon. Clean it often. Filter doesn't need to be inside the tent.
Think outside the (box) tent! lol Put a filter pad outside the air inlet screen.