Based on calls taken during the first year of availability, there are 5 commonly asked questions that dealers have raised about the AccuScan unit. We will cover each in turn.

1. Why does the AccuScan give Free Chlorine and Total Chlorine readings that differ from my DPD No. 1 and DPD No. 3 or DPD No. 4 tests?

The AccuScan can read both total and free chlorine up to 10 ppm. The Wet Lab is limited to 5 ppm, with a decrease in accuracy above 3 ppm unless the sample is first diluted with distilled water. If the AccuScan is giving a reading of above 5 ppm on Free or Total Chlorine and either of the DPD tests are indicating a value at 5 ppm or below, the AccuScan is actually much more accurate in these cases. To confirm this, you may perform a DPD No. 1 and DPD No. 3 or DPD No. 4 test on a sample of 50% distilled water and 50% pool/spa water.

The method and reagent that AccuScan test strips use to measure Free Chlorine is different from the method that DPD No. 1 uses to measure chlorine. DPD No. 1 can give a false positive reading when large amounts of monochloramines are present. The AccuScan Halogen III test strips do not give a false positive reading in the presents of monochloramines. Monochloramines are more likely to be elevated when opening a pool that has been dormant for the winter.

Often you will find the AccuScan reports Total Chlorine as 0.4 or 0.5 ppm higher than Free Chlorine. In other words, the AccuScan picks up combined chlorine that isn’t detected using DPD No. 3 or DPD No. 4 tablets. This is normally due to a small but measurable chlorine demand. Remember, too, that it is possible to have a measurable chlorine residual even with a high chlorine demand, depending where your customer took the sample, the age of the sample, if they had added chlorine recently, time of day, etc.

2. Why are my AccuScan Total Alkalinity readings different from my Wet Lab readings?

We have checked numerous water samples that have been sent by dealers concerned with discrepancies between the Wet Lab titration method and the AccuScan. We can trace the majority of the discrepancies back to two main issues – the dealer’s testing technique (either with the Wet Lab or the AccuScan) and the age of the Wet Lab reagents. Make sure you are performing the tests correctly by asking yourself the following questions:

Are you using a graduated measuring cylinder when determining the proper sample size for the Wet Lab? Rough "guesstimates" are not acceptable at any time!

Never hesitate to ask your Account Manager or a more experienced colleague to show you the correct technique for performing titrations or analyses using the AccuScan. And do not be embarrassed if your titration technique is wrong – many Final Year University chemistry students can’t perform titrations correctly!

3. Why are my AccuScan CYA (Cyanuric Acid, Stabiliser) readings different from my Wet Lab readings? Accuracy of the AccuScan CYA test is highly dependent on the pH, Total Alkalinity and chlorine residual of the sample:

An improved test pad for CYA is in development but is not ready for commercialisation. We hope that we will have a CYA test that is less sensitive to pH, Total Alkalinity and chlorine in the near future. Importantly, the limitations reported above are not problems with the AccuScan unit itself, but with the chemistry of the pad. Note that the Wet Lab test has its own sensitivities and limitations, and there is a constant search for a more viable and accurate CYA test.

Some advice? If your water sample falls into any of the above categories regarding pH, TA or chlorine, or you suspect that the AccuScan reading is incorrect, repeat the CYA test using your Wet Lab. Remember to add Chlorine Neutraliser No. 4 before testing to prevent interference from chlorine or bromine. Remember, too, to take the reading when the black dot first disappears. If you can just make out the black dot, lower the dipstick a fraction – this will give you the correct reading. Once you have the Wet Lab reading, simply overtype the CYA value in ALEX before Saving.

4. Why are my AccuScan Calcium Hardness readings different from my Wet Lab readings? There are several scenarios that may explain some of the variances between AccuScan CH readings and Wet Lab CH readings:

To get accurate results with both the AccuScan and the Wet Lab, proper test technique is very important. Ask yourself the same series of questions posed in Item 2 above. In addition, when using the Wet Lab, ensure that you add the Calcium Hardness Reagent 1B (buffer) first, then the tablets, and that you do not add any more buffer than is necessary.

5. My customer has added Optimiser or Optimiser Plus at the recommended dosage. Why are my AccuScan readings lower than I expected?

The borate test continues to be one of most consistent and best performing tests on the AccuScan. Some of the questions to ask are:

Notwithstanding the advice in this Technical Information Bulletin, Bio-Lab is working to rectify any perceived shortcomings in the current tests. Extensive research is being undertaken with the view to improving the accuracy of the calcium hardness test (especially at levels in excess of 250 ppm), and it is hoped that an alternative cyanuric acid test will be developed that returns accurate results over the widest possible pH range.

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