Gl you've just gone and grown them babies too big.

I think your plants are rootbound. If you aren't using a zyme product then start asap and consider flushing to help get any excess crud/fert build up, old dead roots etc out.
This is something that all of us with waterfarms have run into sooner or later which is why everyone drills extra holes in all their w/f buckets and there STILL seem to be issues which is why I went to 8 inch net pots instead.

There isn't anything you can do really except use your zyme products and try to keep drainage and 02/water flow open for the roots inside your red buckets. If you don't develop root rot problems they may finish ok.