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Product Description (1)

Baquacil® is a pale blue solution that contains around 20% poly(hexamethylene biguanide) sanitiser. When maintained at a level of 25 to 50 ppm, Baquacil is effective in providing clear, clean pool water for several weeks. Unlike chlorine, it is not consumed by organic matter in the pool. With no possibility of chloramine-like compounds forming, odours are markedly reduced. Baquacil, however, has a number of major disadvantages:

  • Polymeric biguanides are highly efficient flocculants which impose additional back-pressures on filtration systems and are liable to be removed from the water along with the solids they coagulate.
  • The range of bacteria that biguanide is effective against is not as substantial as that for either chlorine or bromine. As such, it does not comply with US EPA requirements.
  • Biguanide has no effect upon the growth of algae. As it is incompatible with halogens (see below), hydrogen peroxide must be used as an algaecide.
  • Water is generally dull and lifeless after treatment.
  • Distinctive purple stains form on some pool surfaces, particularly concrete.(2)


For these reasons, biguanide is no longer permitted as a sanitiser for commercial pools or spas in Australia and New Zealand.


Pool Conversion to Chlorination

The potential problems of converting a pool from Baquacil to chlorine merit consideration. Baquacil is not compatible with halogen sanitisers like chlorine or bromine; if any amount of chlorine is added to a Baquacil disinfected pool, a suspension ranging in colour from light yellow to brown will be observed. This occurs because the chlorine forms a stable complex with the biguanide. Sometimes larger "curds" of material can clog the filter, necessitating complete draining of the pool. Most of the finer particulates will be filterable but, quite often, the discolouration and turbidity will persist for a long period of time. Several proven procedures have been developed to handle the Baquacil-to-chlorine conversion; three are detailed below. If followed closely, the time required to get the pool back to a sparkling blue condition can be kept to a minimum.


Method 1 - Draining (3)


Warning - This method may not be suitable for all pools, particularly poorly installed in-ground models where the complete removal of water could cause walls to collapse in on themselves.


1. Drain the pool completely.

2. Apply a mild acid wash to the walls and floor, if the pool surface allows.

3. Before starting the pump, treat with Strip-Kwik and Kleen-It to remove Baquacil from the filter.

4. Refill the pool with water from a suitable source.

5. Test and balance in accordance with the directions given in the Chlorination Start-Up Procedure, below.


Method 2 - Removal of Baquacil by Non-chlorine Oxidation (4)

1. With the filter running, adjust the pH into the range 6.8 - 7.0.

2. Isolate the heater from the rest of the circulation system if possible.

3. Add 600 grams of OxySheen (potassium monopersulfate) per 10,000 litres of water. Broadcast the OxySheen into the pool. Be careful not to get the product on the skin or in the eyes as it can be irritating. If accidentally spilt on skin, immediately wash it off with water.

4. Run the filter for up to 48 hours and backwash if necessary. The pool will be a cloudy green or yellow. Do not be alarmed as this indicates that the Baquacil is precipitating out. Do not add any other chemicals at this stage.

5. After 48 hours, test the pool for Baquacil with the Baquacil test kit. If a Baquacil residual persists, add OxySheen at the rate of 300 grams for 10,000 litres. Continue to filter and backwash if necessary.

6. Check the Baquacil level again. If a residual is still present, repeat Steps 4 and 5 - shock, test, shock - as many times as necessary to reduce the Baquacil residual.

7. When a zero concentration of Baquacil is tested, a "spot check" must be done to verify that no Baquacil remains in the pool:

  • Remove roughly 4 litres of pool water in a plastic bucket.
  • Add 100 grams of Burn Out 35 to the bucket and stir. (Burn Out can be used but sometimes will create a cloud which could be confused with a Baquacil reaction). No precipitate or colour change should be observed.
  • If there is a reaction repeat shock-test procedure (Steps 4 and 5).

8. Test and balance in accordance with directions given in the Chlorination Start-Up Procedure, below.


Method 3 - Removal of Baquacil by Chlorine Oxidation (3)

1. Test a sample of pool water. If metals are present, add Pool Magnet (250 mL per 10,000 litres for each 1 ppm of metals) to the pool water and Quick Clear (as per label instructions) to the filter. Quick Clear is necessary to remove the metals from the system. Do not proceed to Step 2 until all metals have been removed as determined by testing.

2. Adjust the pH to the ideal range of 7.4 - 7.6 using Balance Pak 200 or Lo'N'Slo as appropriate.

3. In the evening, add Burn Out at the rate of 2 bags per 40,000 litres. Pre-dissolve in cool water prior to addition.

4. Allow to circulate for 2-3 hours and then turn off the pump and allow the water to become still. The water should turn a greenish colour, accompanied by the formation of a whitish/tan precipitate. Check that there is still chlorine present in the water and, if in doubt, add more Burn Out.

5. Allow to stand overnight. The precipitant will settle to the bottom and can be vacuumed to waste. If the water is still cloudy and the bottom of the pool is not clearly visible, return to Step 2 and repeat the process.

6. After the pool water has cleared and vacuuming is complete, run filter to remove remaining traces of precipitated Baquacil.

7. Clean filter using Strip-Kwik and Kleen-It to remove any residual traces.

8. Test the pool for Baquacil with the Baquacil test kit to ensure a zero residual.

9. Test and balance in accordance with directions given in the Chlorination Start-Up Procedure, below.


Chlorination Start-Up Procedure (4)

1. Balance the pool as normal by adjusting the alkalinity if necessary then adjusting the pH into the 7.4 - 7.6 range. Add Burn Out at 2 bags per 40,000 litres daily until a stable chlorine residual is maintained.

2. Continue filtration until pool is clear.

3. Backwash the filter and clean it with Strip-Kwik.

4. Backwash the filter well to eliminate any residual Strip-Kwik.

5. Any accessories should be washed to remove any residual Baquacil prior to submerging in the chlorinated pool water.


The number of treatments and the ease of conversion is largely dependent on the quantity of Baquacil in the water. Obviously, the higher the level, the longer and more difficult the conversion will be. Although the procedure for changing a Baquacil pool to chlorine can take a couple of days, it is really quite straightforward.



1. B. Selinger, "Chemistry in the Market Place", 4th edition, Harcourt Brace Jovanovich, Sydney, 1988, pp. 572-573.

2. D. Gray (Bio-Lab, Decatur GA), Fax message to L. Lines, 12 July 1989.

3. D. Leithauser, Technical Information Bulletin, Bio-Lab, Decatur GA, 28 June 1990.

4. D. Starr, Technical Information Bulletin, Aqua-Guard Industries, 1/31 Burgess Road, North Bayswater VIC 3153, 16 March 1988.


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.