Abstract: A passive dispenser adapted for placement in a body of liquid for codispensing a first solution and a second solution in response to a lowering of the level of the body of liquid from a first elevation to a second elevation, the dispenser comprising a first chamber for storing said first solution having an inlet/outlet pathway comprising an interior conduit and an exterior conduit adapted to discharge said solution by siphon flow and further having a vent conduit extending to the atmosphere, and a second chamber for storing said second solution having a refill/discharge pathway comprising a conduit adjacent the chamber and a conduit adjacent the body of liquid and further having venting means, the refill/discharge pathway and venting means being adapted to isolate said second chamber from the body of liquid by means of the formation of air locks.