It can be enlightening to re-read an old post through from the beginning... and in my case, humbling. That RDWC run I was crowing about blew up a week later in a cloud of dead roots, crazy pH swings and obvious signs of root rot brought on by excessive EC. Truth is, I was in over my head with RDWC, and since switching to coco (50/50 hydroton/coco, to be precise) I'm finding things much more stable.
Yet here is where things get interesting; instead of just chucking my whole RDWC setup, I ran it as a base to catch runoff from 5 gallon buckets full of chowmix. To satisfy my own curiousity, I kept tabs on the EC and pH of the water building up beneath the coco buckets and continued to run the recirculating pump and airstones. The water is actually very nice for roots- and several of my ladies' roots are bathing in them, even though they have plenty of coco to grow in.
I switched in part because I had to have something more stable to grow in and because I wanted to add bio-active amendments, which is difficult to do with RDWC. I put stuff like eathworm castings on the coco and run compost teas and pour that on top, and topfeed Canna A & B with more amendments through a very kitbashed irrigation system. This has worked marvelously of late, and yet the plants still seem to be getting something out of the RDWC water underneath.
I've even gone so far as to topfeed the RDWC water and the plants seem to really like it. I know this isn't strictly 'drain to waste', nor is it quite RDWC, but rather something in between. I'm guessing that it works in part because the bennies I'm adding flush through the coco and continually reinoculate the RDWC water, plus nutrients that are washed through tend to be very similar ratios to that given initially.
I'm planning to investigate this approach in more depth in another run soon, and I'll be happy to share the details with anyone interested.
Coco pH; 5.8-6.0
RDWC pH; 5.5-6.0