Why are my plants yellowing
 

Hello Ron!!

Why are my plants yellowing towards the end of the flowering cycle? I'm using an all-round nutrient pre-mixed solution, is this the best thing to do? Also, while you're there, which hydroponics system of growing do you think is the most energy efficient? Thank you, from Peaches.

I would increase the strength of your solution. The big lower fan leaves do turn yellow in the flowering stage because they aren't needed anymore and should be removed.