I have grown like that once. Just like ForgetClassC said I used another bucket when changing nutrients.
When the plant starts drinking a lot I stopped changing buckets. It seemed to drink a bucket in a day or two. I just topped fed the plant with the proper nutrients and let it drain to the bottom.

I just re-read your post, you do use two buckets, its when you are changing the buckets you are having trouble... Your root mass must be massive.
Mabey next time drill a hole in the bucket you can use as a drain and then just top feed the nutrients so they fall to the bottom.
The picture looks good. I was actually wanting to see how much it stretched. It did not stretch to much. That is a good thing. The LED light you are using is working nice.
Thank you for posting a picture.