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Product Description (1)

The Questa PoolFresh® system uses the electrolytic generation of copper and silver ions to prevent microbial activity in pool water. A low current (< 150 mA) is passed across two diecast copper-silver alloy electrodes within a PVC housing, the latter replacing a 90° elbow in the existing plumbing of the filtration system. Polarity of the two electrodes is switched every 90 seconds to ensure that both undergo oxidation to the same extent. This switching is indicated by a red/green LED on the PoolFresh housing. Automatic regulation of the current maintains metal ion levels within specified limits; 0.3 to 0.9 ppm for copper and 0.01 to 0.05 ppm for silver. Life expectancy of the sacrificial electrodes is estimated at between 1½ and 2 years for the "average" pool.

 

Oxidation is promoted using PoolFresh Plus®, a proprietary peroxygen compound (possibly based on sodium peroxide) that is added to the pool water every 10 to 14 days during summer and once a month during winter. The addition of 500 grams of the solid material per 50,000 litres of water is reported to give a residual level of around 2 ppm. As for residual chlorine, testing can be performed using the standard DPD #1 colorimetric procedure.

 

Documentation provided includes the results of comparative testing performed by the NATA-registered laboratory Analchem-Bioassay Pty. Ltd. of Lilyfield, near Sydney.

 

Precautions and Limitations (1)

The PoolFresh documentation lists a number of limitations to its use and application:

 

  • Copper levels must be tested periodically to ensure that the concentration does not exceed the 0.9 ppm maximum. If high, the unit must be turned off and the copper allowed to return to acceptable levels; this may take several days (see Critical Assessment of Claims, below).
  • Although reportedly less sensitive to pH change than chlorine, pH levels still need to be maintained at between 7.2 and 7.6 using sodium bicarbonate. The mass of bicarbonate added daily should not exceed 1 kg.
  • Additives such as Baquacil and bromine are incompatible with the PoolFresh system and must never be used. Bromide anions from reduction of the latter will combine with the silver ions generated by the PoolFresh unit, resulting in an insoluble precipitate of silver bromide.
  • Although the PoolFresh system is compatible with chlorine, the latter being recommended by Questa to remove heavy staining due to plant material falling in the pool, undiluted hypochlorite must never be added directly (see Critical Assessment of Claims, below).
  • Alum must not be used as a water clarifier as it absorbs copper and silver ions out of solution.
  • Cyanuric acid (CYA) will inhibit performance if in excess of 50 ppm. Dilution must be carried out prior to running the PoolFresh unit. 

Critical Assessment of Claims

Reservations expressed in previous TIBs on the Floatron® ioniser (2) and ionisers in general (3) are valid here. There are also a number of significant errors and omissions in the PoolFresh documentation.

 

1. High bacteria kill rates compared with chlorine. This claim is partially justified by Analchem Bioassay's testing. (1) Results do show more rapid killing of Escherichia coli and Pseudomonas aeruginosa but, as reported in other studies (see TIB BG-016), this general trend does not apply universally to all forms of bacteria, algae, fungi or parasite.

2. Calcium (read chloride!) and copper ions combine to form insoluble copper chloride. Copper(II) chloride is quite soluble (706 grams per litre of water at 0°C) (4); it is silver chloride that is almost totally insoluble (0.00089 grams per litre of water at 10°C). (5)

3. Conversion of salt water pools to the PoolFresh system requires emptying and refilling with fresh water. Whilst this is correct, the Comparative Testing Program document does not state that this is to avoid insoluble silver chloride formation (again), nor does it point out that some tap water (particularly that in Adelaide and its environs) is so heavily chlorinated that residual chloride levels will cause significant silver chloride precipitation. The result could be a very cloudy pool!

4. Silver cannot easily be tested with a colorimetric test kit. There are a number of quick and relatively precise methods for the determination of silver in solution. One possibility is a turbidimetric test similar to the existing technique used in cyanuric acid determination. The silver-containing solution could be treated with a chloride reagent, forming a silver chloride suspension. A calibrated dipstick could then be used to approximate the level of silver in the sample. Using adsorption indicators such as fluorescein or eosin (the bright red dye often used in staining biological samples for microscopy), titration with a standardised chloride or bromide solution is also feasible. The endpoint of the titration is observed by a colour change from yellowish-green to pink for fluorescein, or from pink to violet with eosin.(6) The downside of this procedure is that difficulties arise detecting the colour change if the sample is significantly discoloured to start with

5. Where a residual copper level is present, it is safe to assume that a corresponding level of silver is also present. This claim is made on the basis of the electrode alloy's composition. There are problems, however, with making such an assumption. Based on electrochemical principles, the rate of copper ion production will not be the same as that for silver. Apart from requiring 2 electrons to produce a copper(II) ion, compared with only 1 electron for each silver ion (see TIB BG-016 for background), the standard reduction potentials for the two metals are quite different; +0.337 V for copper and +0.799 V for silver at 25°C.(7) More intriguing, however, is the fact the both electrodes are identical in composition. During the first 90- second cycle, one acts as an anode, the other as a cathode. During the next 90 seconds, the polarity is reversed; the anode is now a cathode, and vice versa. Why then doesn't the copper and silver start plating out on the cathode each time? No doubt it does to an extent. The question that then arises is whether this superficial plating is of the same copper:silver ratio as the bulk alloy in the electrode. If not, the rate of copper and silver ion production will continue to change over time.

6. PoolFresh Plus has enough oxidation potential to maintain silver in a high state of oxidation, thereby creating an extremely powerful bactericide. This claim is true, but the term "high state of oxidation" is misleading. Silver exists in three oxidation states; 0 [silver metal], +1 [silver(I) or argentous ion] and +2 [silver(II) or argentic ion]. However, the silver(II) ion is highly unstable and does not exist in solution. Therefore, the only pertinent species here is the silver(I) ion. As noted above, the standard reduction potential for silver is +0.799 V at 25°C. (7) The equivalent potential for acidified hydrogen peroxide is +1.776 V. As the latter is the higher of the two then, assuming peroxide is the main component of PoolFresh Plus®, the silver will remain ionised rather than undergo photoreduction to silver metal (the latter would present itself as a very uninviting black precipitate at the bottom of the pool). One footnote to this. If the peroxygen blend does contain peroxide, the claim made in the Comparative Testing Program that PoolFresh Plus is "non-toxic" definitely only applies when dissolved in water at the recommended dosage level. Apart from being highly corrosive, peroxides can cause nausea, vomiting and, in severe cases, massive internal bleeding if ingested. (8)

 

Conclusions

As in previous Bio-Lab communications relating to ionisers, the jury is still out on whether they satisfy all the requirements for a stand-alone pool water purification system. When compared with the Floatron solar-powered ioniser, the Questa PoolFresh unit would appear a somewhat more reliable device, both from having automatic control of the rate of metal ion production and not being dependent upon the availability of sunlight to function. Furthermore, the Questa documentation,1 although flawed in several places, does admit to shortcomings in their product. However, apart from the dubious benefits of copper and silver ions over chlorination, one major reservation must remain

 

References

1. Questa PoolFresh Sales Brochure, Operating Instructions and Comparative Testing Program, Questa Pool Products Pty. Ltd., 12 Churchill Street, Silverwater NSW 2128.

2. "Floatron® Solar-Powered Ioniser", Bio-Lab Australia Technical Information Bulletin BG-042.

3. "Ionisers", Bio-Lab Australia Technical Information Bulletin BG-016.

4. R.C. Weast (ed.), "CRC Handbook of Chemistry and Physics", 57th edition, CRC Press, Cleveland OH, 1976, p. B-110.

5. R.C. Weast (ed.), reference 2, p. B-156.

6. J. Bassett, R.C. Denney, G.H. Jeffery and J. Mendham, "Vogel's Textbook of Quantitative Inorganic Analysis", 4th edition, Longman Scientific and Technical, Harlow, Essex, 1986, pp. 281-288.

7. D.A. Skoog, D.M. West and F.J. Holler, "Fundamentals of Analytical Chemistry", 7th edition, Saunders College Publishing, Fort Worth TX, 1996, pp. A12-A15.

8. G.D. Muir, "Hazards in the Chemical Laboratory", 2nd edition, Chemical Society, London, 1977, p. 283.

 

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.