In my experience the plants sitting in the runoff is not a problem, all of my cabinets have a bottom tray that the pots sit in to catch the runoff. I don't use an enzyme or anything else as there is no need.
Think about how plants grow in the wild - they put their roots down as close to the water table as they can. Yeah, if the plant sits in water up to the trunk bottom the trunk will rot and the roots will drown and die, but if the bottom roots hit water they allow the plant to uptake as much as it needs without damage. Consider those of us who run hydro - those plants roots are in water all of the time and they do just fine.
I used a water cloner for years to root cuttings without any problems either, though the aero is faster and more effective.
The key here is simplicity, the proof of this systems efficiency is what you see after 3 months - 9 & 1/2 ounces of AK 47 bud from a 250 W HID cabinet. If it didn't work I wouldn't use it. :) If it needed to be more complicated I would say so and tell you what else is needed, but I don't need to as this is all there is to it.
This irrigation system - though you have to mess around with it to get it set up right initially - is cheap, easy and reliable. Nothing else really need to be added to it unless you want to make it more complicated and expensive, but that is another thread. ;)