Treatment of swimming pool water

A method of removing dissolved phosphate from the water of a swimming pool, where the swimming pool is fitted with a filter, means for circulating water from the pool through the filter to remove particulate matter from the water and means for backwashing the filter, the method including the steps of:

• introducing into the filter or forming in situ within the filter a particulate reagent comprising a lanthanide or yttrium carbonate which is (i) substantially insoluble in pool water at pH 6-8, (ii) adapted to be retained within the filter, and (iii) adapted to react with dissolved phosphate in the pool water to produce a substantially insoluble particulate reaction product including phosphate, said reaction product also being adapted to be retained in said filter,
• circulating water from the swimming pool through a filter to bring the water into contact with said reagent to form said reaction product within the filter, thereby removing dissolved phosphate from the pool water, and
• backwashing the filter.

In a swimming pool system including a pool of water, a filter and pump means for circulating pool water through the filter, the method of removing dissolved phosphate from the pool water comprising the steps of:

• introducing into the filter a finely divided particulate reagent comprising-a composition including lanthanide, yttrium, zirconium which is substantially insoluble in pool water at pH 6-8 and which is adapted to react with dissolved phosphate to produce a substantially insoluble particulate reaction product, said particulate reagent and said particulate reaction product each being of a physical form such that each is adapted to be substantially retained by the filter, and
• employing the pump means to circulate pool water through the filter so as to contact said particulate reagent retained within the filter to form said reaction product within the filter, thereby removing said dissolved phosphate from the circulating pool water.