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This Technical Information Bulletin was prepared following several instances of consumers mixing undiluted Back-Up with Back-Up II prior to adding to their swimming pool, only to find a blue gelatinous substance deposited in the bucket. On at least three occasions, the consumer thought nothing amiss and poured the contents of the bucket directly into the pool water. The result was a collection of undissolved blue globules on the pool floor.

As discussed elsewhere,(1) Back-Up II is a long-lasting algae inhibitor utilising Bio-Lab's patented copper polyacrylate technology.(2) One of the constituents in the product is a high molecular weight polyacrylic acid that provides longer term stain protection than is possible with the MSA II formulation. This compound is negatively charged. The active constituent in Back-Up is a blend of alkyldimethylbenzylammonium chloride salts, also referred to variously as "benzalkonium chlorides", "quaternary ammonium compounds" or, simply, "quats". These quats are positively charged. When Back-Up is mixed with Back-Up II, the polyacrylic acid is electrostatically attracted to the quats, forming an insoluble polymer. In the absence of copper, this polymer would be colourless or white. Due to the presence of copper in Back-Up II, the polymer takes on a bluish appearance.

The same insoluble material will form if Back-Up is mixed with undiluted Salt Pool Protector or MSA II . However, given that the confusion appears to have arisen from the similarity in names (Back-Up versus Back-Up II), this is an unlikely scenario. It should be added that pouring Back-Up II, Salt Pool Protector or MSA II into a pool previously treated with Back-Up will not result in the deposition of this blue material as the concentration of quat in the water is far too low (usually much less than 10 ppm). The reaction will only occur in the presence of concentrated Back-Up; that is, either straight from the bottle or diluted in a bucket of water.

In the three instances where the consumer proceeded to pour the blue material from the bucket into the pool, it was found that the globules did not adhere strongly to the pool floor and could be removed easily by scooping out with an appropriate utensil. Any traces remaining dispersed into the pool water over a short period of time, most probably being trapped in the filter and removed at backwashing. As an aid to breaking the polymer down quicker, it was suggested that the consumers shock dose the pool with Burn Out 35.

Clearly, the above is a classic example of consumers not reading labels carefully. Two of the mandatory (3) Safety Directions on many BioGuard product labels are "Do not mix with other chemicals" and "Mix with water only". In this instance, the result of not following this advice was benign. In other cases, the result could be much more serious - possibly even life-threatening.


1. "Algae Prevention Using BioGuard Back-Up II and Salt Pool Protector", Bio-Lab Australia Technical Information Bulletin BG-068.
2. J.P. Garris, US Patent 5,541,150 (Dated 30 July, 1996).
3. Australian Health Ministers' Advisory Council, "Standard for the Uniform Scheduling of Drugs and Poisons", No. 15 (Effective Date - 1 July, 2000).

The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.
TIB No. BG-078
Site maintained by Greg O'Connell
Last update: 30 April 2003