The system will last a long time, and the only thing you would have to add is additional water to the system (with electrolyte).  There is an enormous about of stored energy in the water (HHO - two parts hydrogen and one part oxygen), so just a small amount of water can be used to generate oxyhydrogen gas for a long time to improve the fuel efficiency of your vehicle.

Over time, you will want to open the system and clean it, with soap and water.  It takes perhaps 5-10 minutes every six months.  You don't have to clean it very well as this isn't surgery, but it is good to do this to keep the production of HHO maximum and make sure the tubes are completely clear so there is a maximum flow of oxyhydrogen HHO) to the air intake of the engine.

Ryan
Run Auto With Water Mechanical Support
http://www.runautowithwater.com