Here's what I say about the nute transition. I'll tell you what I'm doing in my current grow... and then what I think you should do. I just switched to 12/12... gave them a 36 hour dark period before the lights came back on. When the lights went out I changed the nute solution from 100% veg nutes (and additives)... to 2/3 Veg Nutes and 1/3 Flower Nutes... and I'm still using veg additives (I think it's lame that companies divide up additives between veg and flower... I think it's just for more money... AN has two cal-mag's). I will use this 2/3 - 1/3 mix a for about 4 days... then I'll bump it up to 1/3 Veg Nutes, and 2/3 Flower Nutes... and start with the flowering additives. Then 4 days later (or when pistals start showing) I'll change the mix to Full flower nutes.
I would suggest you make one transition. So I would start 12/12 with the veg nutes you've been using all along (the first 10-14 days of 12/12 are vegging anyways)... then maybe 6-7 days into 12/12 I would go 50/50 with the veg/ flower nutes. Then when the flowers start showing I would switch to flower nutes.
I suggest the 1 change becuase I am using 1 gal rez.... so an extra change doens't waste much water or nutrients... but my bigger rez I would do what I suggested to you. Also I am changing mine every 4 days becuase I expect my girls to show flower a lot faster. I don't know if they will, but the BushMaster I used is supposed to cut that veg under 12/12 time out. We'll see.
Whatever you do... don't do what I did my first grow. When I started 12/12 I dumped the rez and filled with 100% flowering nutes. Not like it messes anything up.. but they aren't using that stuff yet... plus becuase I (and you) veg so short compared with flower, our flowering nutes will go alot faster than the veg, so wo might want to try to conserve the flowering stuff a bit. I think my veg nutes are going to last me 2 years, while I'm almost out of the flower nutes halfway though my second grow. My ph adjusters are like that too. I bought a gallon of pH up and pH down. I have used about 300 mL of the pH down... and about 3 drops of te pH up. Don't think I will ever in my life use my gallon of pH up, haha.
Sorry long story. Plants are looking amazing my man.
And I love the filter... that is some cheap ass stuff. Did you wrap the carbon in a tissue??? Got the cheap ass Home Depot fan, re-using the box. So ghetto, i love it.