Control of algae in re-circulating water systems

Claim 1

A water re-circulation system comprising: an open tank, which contains a body of water, which is open to sunlight and to the atmosphere; feed and return pipes connected to the tank; where the system is arranged so that the water, when in the tank, moves only imperceptibly during re-circulation, but the water, when in the pipes, moves at a rapid bulk volume flow rate during re-circulation; a plastic jacket; where the jacket is installed in and as part of one of the pipes and comprises a cylindrical sleeve of larger diameter than the pipe, each end of said jacket being connected to the pipe by a pipe-to-sleeve adapter which is a snug fit to the sleeve; where the jacket has means defining an inlet and means defining an outlet connected into the said one of the pipes to accommodate the whole through-flow of water in the said one of the pipes; where the jacket, apart from the inlet and outlet, is enlosed and sealed and capable of sustaining an internal water pressure; substantially pure metallic zinc; where the zinc is mounted in the jacket as a plurality of discs which are disposed co-axially with the sleeve so as to be well-exposed to the water that flows through the jacket; where the discs are located in the sleeve by virtue of their being trapped therein between the two adapters; and where the jacket contains substantially no other metal than zinc exposed to the flow of water through the jacket.