Well, you really shouldn't use silver kill coils and a liquid based biocide. Annoying side effects can occur, depending on the situation.
Anyways, If you have just distilled water and a biocide all you need to do is put about a drop of the liquid biocide in every month or so. It's a good idea to drain your loop every 6 months, then flush it with distilled water and maybe a bit of cleaning agent., then refill it with some fresh coolant. That's not always a necessity, but it's generally a good idea. (Unless you're using a high end/expensive coolant such as Mayhems pastel. Then the price of coolant becomes a factor)
It's a good idea to disassemble your loop, and clean it every 12 to 18 months. This is assuming problems don't occur, if your flowrates drop and something might be clogged of course you need to disassemble it to clean it, that's a given. If, however, no problems occur in a year through a year and a half, which is much more likely, it's still a good idea to disassemble it and give the waterblocks a good cleaning.
People who complain about not going to liquid cooling because of the maintenance over exaggerate it. There really isn't that much maintenance, unless you do something stupid and mess up your loop. But that usually doesn't happen when people do their homework.
Anways, I guess to sum up the answer to your question. Drain your loop every 6 months and refill it. Then every year or every year and a half disassemble your blocks and give em a good cleaning.