In my opinion, you can never keep a res sterile. Chemicals you put in will inhibit microorganism growth to a point, but will never kill 100% of everything in concentrations that are safe for plants roots. Both roots and microorganisms are living cells, and although roots are tougher, chemicals have no way of distinguishing and selectively acting on just one type of cell.
What you are actually doing is puting a concentration of chemicals that is near the sweet spot where roots will not be badly affected, but microorganisms will be sufficiently suppressed not to take over everything betweeen res changes. If you already have slime, that approach might not work because you'll always have spores living in there (no mater how well you clean they'll be there, trust me), and little other microorganisms on the roots mean once those spores hatch there will be nothing stoping them from taking over everything really fast once your chemical concentration drops just slightly or there is sufficient food that they can multiply faster then the chemical is killing them. That's why people using H2O2 sometimes see it fail after some time.
I'm no RDWC or sterile expert, but that's what I got from reading on the forums about this topic...
Also, as I said, I'd be careful aout adding silver for a long period of time as it acts in a way similar to heavy metals, acumulating in organisms over time and poisoning its tisues.
Two question on this topic..First I will start with saying I am using DWC (not recirculating) with GH Flora series and I've got the slime mass and brown algae.