Q: Do you know how to lower the calcium hardness in swimming pool water?
A: Get your water tested by another clerk
Over here I've seen Bioguard and their ALEX system and Taylor.
The way the tests are performed, the accuracy of the measurements, the adherence to "good practices" (ie cleaning the equipment, recapping, holding the dropper bottles properly, perform the test slowly etc) all these have a major impact on the results.
And it's not just "using" a kit, you have to know your test kit, know its limitations, know the possible interferences, know how to handle "extreme" situations (high FC, high CH, low TA etc) and how they influence your testing protocol and testing results.
Then you get customers who bring in water samples in pickle jars and Pepsi bottles (even saw one bring water in the big blue scoop you use for chlorine), didn't wash their hands before taking a sample, didn't rinse the jar, took the sample by skimming the surface right near the return, that sort of thing.
Back in 2008 I investigated about 6 stores to see how they performed. I saw CH and CYA tests that were done way too fast, dirty and soiled equipment, poor lighting, stopping the titrations before the endpoint, incorrect sample volume, not using all the prescribed reagents, using the reagents in the incorrect sequence. The pool stores invest all this money in testing equipment, and labs and can't even use the thing properly.
The clerks don't know what's happening with the tests (ex: they don't realize that the TA test is an acid demand test, they don't know what R-0001 does etc) They're not fluent with the material. They should be forced to read Standard Methods.
They should know enough about the chemistry to visually and convincingly demonstrate the effects of adding borates (or bicarb) to a customer using the comparator and a few reagents.
So there's wrong testing, therefore wrong results therefore wrong treatments are suggested. And for that last one, the treatments, the pool store clerks usually drop the ball again by suggesting and saying things may be totally wrong (there's another thread on this somewhere).
Staff training is usually done by another staff person who got his from another staff person etc. Like playing telephone, errors and omissions creep in along the way.