@TriangleMan help us our here. Can you add your recent, real world experience ?
Happy to. I just recently had to clean up the mess Leslie's left me with after sinking hundreds of dollars into their worth-than-worthless-because-they're-actually-detrimental solutions to non-existent problems.
I'm an engineer by trade, so inclined to follow the data and make fact-based decisions. Who better to guide me in properly caring for my new pool than the pool store, right? They use fancy testers that are better than the color strips that match none of the standards printed on the bottle, and must be better than my basic old-school two-way chlorine and pH drop test right?
I won't bore you or embarrass myself with all the chemicals I naively purchased on their advice both before and after the pool first turned cloudy following their recommendations.
I started to realize something was wrong when I began questioning their recommendations once the algae appeared. They very nearly convinced me to drain my pool based on a CYA reading of 115, only to come back and tell me days later that it was 46, in spite of never draining the pool. I then confirmed a wide array of mismatched readings and even more mismatched recommendations at various other pool stores based on the exact same water sample. The truth, I found out when I got my own test kit, was actually just over 30!
As an engineer, I attribute that error to an equipment calibration issue, most likely, although operator error is certainly possible. (Could even be contamination.)
If they can't calibrate it for their own tests, do you think they'll be giving you a properly calibrated machine or the instructions and ability to calibrate it?
To be certain, I'm sure there are some good pool-store techs who care about quality, but most of them are probably just clerks passing time on their way to something better or just trying to collect a paycheck to get by. They're not invested in or passionate about /your/ pool. How would you be able to sort the good ones from the bad? And that's the charitable take.
Better, I've learned, to do your own tests with a more fool-proof system. Trust no one but yourself (and double-check yourself too!)
What do you have to lose? $70 for a good test kit? You'd make use of it anyway. If you're putting $30 in chemicals into the pool every week already, the marginal cost is small.
Worst case, you learn that it's not hard to be much more reliably accurate than they are, with the added benefit of knowing what's going on with your pool and why.
You don't want the "pool store level tester." You want better. And it really is easier than you think. (Even just think of the time you'll save driving over there and waiting in line.)
As for that $30/wk. If your CYA really /is/ 150ppm, then 4-6 gallons of chlorine a week in a 36k pool might not be nearly enough.
That's maybe 20 ppm over a week, when your FC level should be close to something like 19 or 20 as a target range in the first place and, in my experience, I lose something like 25% to 33% of my FC per day (up to and over 50% when I had to SLAM courtesy of Leslie's).
I'd say:
1) Get your own test kit ASAP
2) Verify that CYA level yourself before you do anything else
3) Adjust it if necessary sooner rather than later. If you wait until fall, you're likely to be battling algae all summer.