Yo again PDT,

You are talking NFT/fog here. Flow of water on the bottom of the rails, to feed the water roots and introduce fog to hopefully get fine roots near the top.

I did NFT years ago, using plastic gutters that had plastic covers. Holes drilled in the covers for 3" net pots. You will find that once the roots reach the bottom of the gutters or rails it will dam up the return water very effectively. I'm not sure that adding hydrotron will help or make worst that problem. I had to place perforated right-angle material on the bottom of the gutters to insure a return to the rez. (I found I could "dam-up" over 20 gals of nutrient solution in 24' of gutter). This led me to adding the drain channel, and also led me to use misters in the top of the gutter trays. It is also the last grow machine I built that used a recirculating system and resevoir.

BTW, left an answer about the 3" collars....but was just thinking now, why not use 2" net pots and blackstar collars? I'm pretty sure you could grow just as large with the 2" as a 3".