Hey man sorry it took me a couple of days to reply but according to Jorge Cervantes he says to flush with 3x the amount of soil but I myself do 1:1 or a little bit more. I find that 9 gallons of water to flush a 3gal bucket to be kind of ridiculous. Don't forget to ph your water before flushing 6.3-6.8 ish. Check your run off water and average the run off and the ph of your flushing water and I believe that gives you a better idea of what ph your soil is. I just flushed my mother in a 3gal with about 3 gals of water. Put her in a 5 gal bucket and use a pot to make a gap between the floor and your plant and it all just falls down and you don't soak your soil in the crap.
If you know about "Al B. Fuct" he documented that pk13/14 at wk 3 was giving him bad results and if you do some more research on his grow style you'll see that he makes everything completely simple so while I don't think a couple of drops will hurt it I think you may be just wasting precious $$nutes$$. If you see your plant get starved of P and/or K then maybe start adding a couple drops before wk 5
. It's all about keeping it simple for me now that I mirrored Al's grow... just watch your plants and catch deficiencies Then give em what they want. Then clone those and run them over and over with perfect results. As far as the yellowing stay on top of it and watch the progression, maybe you will have to bump up your bloom ppms.
From what I read Skunk#1 is very hard to kill so you should be good no matter what you do lol.
I recommend picking up Jorge Cervantes' grow bible. It's definitely not better than forums but it is a Great reference book for personal use. I still find myself looking into it at least every month.