A tip for Spa Owners that use chlorine and or bromine is an effect on water testing called bleaching. This is when the chlorine and bromine levels are extremely high making the pad on the Test Strip reading the sanitiser level or other testing method either a tablet or liquid test reads Zero because the sanitiser level is so high it corrupts the test by making the Colour disappear. This can lead you to think that there is no Chlorine/Bromine in the water so you add more!
Bleaching is hard to pick!
If you can smell lots of sanitiser or the pH reading is showing an extreme purple colour or for whatever reason you are concerned that bleaching is occurring do a Dilution Test.
Take a fresh sample and dilute it say by half with bottled water, shake thoroughly and compare this to the initial test. If a colour suddenly appears on the 2nd test after no colour on the 1st test, your water may have excessive levels of chlorine or bromine.
If this is the case you should add Lo-Chlor Chlorine/Bromine Remover roughly at the rate of 8 grams per 1,400 litres to remove 1 Part Per Million of Chlorine/Bromine. Retest 2 hours later.
Excessive levels of chlorine can occur when old style non ORP controlled salt water chlorinators were installed on Spas. Some of these chlorinators had a booster button on the unit which when pushed allowed the chlorinator to add via an internal timer a “Hit” of chlorine. If the chlorine was already high then this booster could have injected enough chlorine to bleach the testing strip. If you believe this may be the case please perform a Dilution Test as described above.