I will second the opinion that local and chain stores generally aren't trying to rip you off. What they are trying to do is sell high priced pool branded products based on testing that in many TFP members experience is hurried and inconsistent (day to day and store to store). Testing is typically based on methods that do not provide a high enough degree of precision (not much is required, but they are too far from what is necessary).
If I had to give a general opinion of many pool store customers attitudes it would be as follows: They are in a hurry to get their water perfect, do not want to be 'confounded or confused' with the chemistry. If the stores tried to educate every customer on the finer details that take about 4 to 6 hours to figure out and another 4 to 6 to confidently put into practice, their sales would decline because they would be focusing on teaching instead of selling. Every time I went to my pool store at least one person in the testing line had a green mess to deal with and blindly purchased the magic bullets of varying colors and price.
I would encourage the OP to read some of the end of season success stories in the TFPC forum, mine included -
thanks-to-everyone-who-contributes-here-t70792.html as I had a similar desire to reduce costs. My first year I was happy to be using the high priced treatment program my locally owned store had sold me which seemed to be doing the job, along with the other weekly chem additions to bring the various numbers in line. At the end of that year I was somewhere north of $800 in the weekly shock/tabs/algaecide and other additions and questioning whether it was worth it. I later switched from their chems to a cheaper program from a big box store. Mid season my pool store identified an issue they did not expect to see based on the chems they thought I was purchasing from them - high CYA.
The store spotted the issue and their alert made me wonder what I was doing to my pool and the downside of my decisions on what to add. I learned more in the Pool School and figured it out. I suspect that the OP's BIL has no idea he is near the edge of a potential algae bloom, or perhaps he is draining or vacuuming to waste weekly keeping CYA barely under control.
With the proper test kit and what I learned here, I am saving money and in control of my pool. I works for me, but your mileage may vary.
I would suggest the OP do what they are comfortable with and also be very careful with purchasing a kit from Leslie's as the only two that will suffice and allow control are their item numbers 81329 and 81325 which are not stocked in the stores near me and must be ordered.
Good luck and happy swimming.
(depending on ages of course)
