I would suggest just using the recommended amount of sodium hypochlorite (Clorox bleach to you non chemists, or Javex to you Canucks) in the tank. As Chris said you can find the details for the exact level (I forget) using the search function.
But more importantly, be sure to USE the water system. By that I mean that anything you put in the tank (like clorox) will not help the entire system unless you pump that treated water throughout ALL the pipes frequently. Water standing in the pipes looses its chlorination treatment quite quickly, and only by pumping fresh water through will you keep the system sweet.
A side note. Each spring I would commission the water system by pumping out the antifreeze (which never bothered me by the way) and filling the tanks and water heater with fresh city water in May. But then the water in the hot water tank would sit, hot from all the engine use, til August when I would go on my cruise. We didn't sleep aboard at the club, so we never used the hot water till then. By then it had developed the sulfur odor that showed the city chlorination was no longer effective, and bacteria were growing in the tank. It is a simple - but NOT easy - process to shock the tank with bleach to get rid of the odor, but what a pain.
So for a couple of years I made point each weekend when I went for a daysail to be sure to pump some water from the hot water system at the end of each day, just to get fresh still-chlorinated water from the main tank into the water heater. That did the trick and stopped the sulfur odor from developing, but was also a royal pain to do.
So the last few years I just didn't fill the water tank until right before the cruise. The manual says to NEVER use the engine without water in the tank, but near as I could tell it didn't make any difference. YMMV.