The water in many industrial and recreational recirculating water systems such as cooling towers, swimming pools, spas, ornamental ponds, plumbing, pipework and other surfaces and the like is susceptible to infection by microorganisms such as bacteria, algae, yeast and fungi. These organisms may be pathogens or potential pathogens. Thus, for safety reasons, it is highly desirable to control their growth by the addition to the water of sanitizing agents. It is also desirable for aesthetic reasons, to control the growth of non-pathogenic bacteria, algae, yeast and fungi, particularly the so-called “nuisance” algae, yeast and fungi which cause discoloration and/or staining of the water and surfaces in contact with the water A variety of sanitising agents have been employed for controlling undesirable micro-organisms in recreational recirculating water systems. The most common sanitising agents provide free chlorine and/or bromine (typically at a concentration in the water of 1 to 5 ppm free halogen). Chlorine may be provided either directly as chlorine gas or sodium or calcium hypochlorite or via a chlorine release agent such as a chlorinated isocyanurate or chlorinated and brominated hydantoin. Chlorine may also liberated in situ by electrolysis of sodium chloride. Other sanitising agents which have been used in such systems include ozone, ozone forming chemicals, hydrogen peroxide, hydrogen peroxide forming chemicals, copper and/or silver salts which provide copper, silver or chelated copper ions (typically at a concentration in the water of 0.1 to 1.0 ppm), quaternary amines and polymeric biguanides, especially poly(hexamethylene biguanide) (hereinafter referred to as PHMB) which is typically used at a concentration in recreational water of 6–10 ppm. Systems employing ultra violet light have also been used to sanitise recirculating water. Sanitising agents are used at higher concentrations in industrial recirculating water systems and additional sanitising agents may be used including but not limited to 2-methylisothiazolinone, 5-chloro-2-methylisothiazolinone, benzisothiazolinone, 2-bromo-2-nitropropane-1,3-diol, 1,2-dibromo-2,4-dicyanobutane, methylene bisthiocyanate, 2-(thiocyanomethylthio)-benzothiazole, formaldehyde and formaldehyde release agents, glutaraldehyde, dibromonitrilopropionamide and bromo-hydroxyacetophenone or mixtures thereof.
Although these primary sanitising agents are very effective in controlling bacteria they do not always provide consistent control of the so called “nuisance” algae, yeast and fungi which can cause discoloration and/or staining of the water and surfaces in contact with the water.
Examples of “nuisance” algae which are found in swimming pools include eukaryotic and prokaryotic algae, for example green algae (e.g. Chlorella spp.), black algae (e.g. Phormidium spp.) and mustard algae (e.g. Eustigmatos spp.). Of these, we have found that mustard algae are particularly difficult to control, regardless of the type of primary sanitising agent used. They appear as slimy deposits attached to the pool sides and bottom, as well as in the plumbing and in the filter, and vary in colour from dark green to brown.
Examples of “nuisance” fungi (often referred to as mold) isolated from swimming pools include Aspergillus spp., Cladosporium spp., Mucor spp. and Paecilomyces spp. Paecilomyces lilacinus is the causative agent in so-called “water mold”, “pink mold” and “pink algae”. P lilacinus can manifest itself as white, grey or pink slimy deposits that are found in niches such as under ladder steps, in skimmer and pump baskets, in filters and piping. P lilacinus is also found growing in recirculating water filters where it can have an adverse effect on the efficiency and lifespan of the filter media. In its mature form, the fungus can also attach itself to pool surfaces and cause chronic turbidity problems which are difficult to control.
Examples of common “nuisance” yeasts found in swimming pools include Saccharomyces and Candidia species.
The wide spread occurrence of “nuisance” algae and fungi has lead to the introduction of methods of controlling these persistent microbes such as dosing with larger amounts of the sanitiser, shock dosing with chlorine or the introduction of further sanitisers or additives such as chelated copper, copper sulfate, combinations of chlorine and ammonium sulfate, colloidal silver, linear and/or cyclic quaternary amine compounds and polyquaternary amine compounds. However, these methods and algicides/fungicides have shown only limited efficacy against the “nuisance” algae and fungi and can give rise to undesirable levels of foam, especially in re-circulating water systems such as spas. Furthermore, in some circumstances, the additives themselves (especially chelated copper and copper sulphate) can cause staining of surfaces in contact with the water.
Any agent to be added to a recreational water system to control bacterial growth and “nuisance” algae, yeast and fungi must meet a number of demanding performance criteria. These include:    a) an excellent toxicology profile;    b) reasonable solubility;    c) freedom from unpleasant taste;    d) odourless or free from unpleasant odours (post addition);    e) non-staining of the construction materials e.g. plaster, plastic;    f) stability to light;    g) stability to other additives present in the water (e.g. sanitisers, H2O2 and EDTA);    h) little or no effect on foaming; and    i) no adverse effect on water appearance e.g. discoloration or turbidity.
Thus, there is a need for a method of treating recirculating water systems to control not only the growth of pathogens, potential pathogens and other bacteria, but also the growth of those “nuisance” algae, yeast and/or fungi which persist in the presence of a primary sanitizing agent.