Shaney, I have to say a couple things. Nothing is absolute. Adding too little of something to pool water--with the exception of chlorine--is not a problem. Adding too much, though, can be bad. CYA, for example. It just doesn't go away, so you have to drain out some water and refill, thus diluting all the other stuff in the water. I noted that your pool store guy told you that. You don't always get good advice like that from a pool store, but you did, so the blanket condemnation of pool stores may not be appropriate. Someone else here suggested under-adding of stuff. I pretty much always do that (again, except for chlorine.) This is not a one chance only deal. You add a little acid and tormorrow you test again. Still low? Add a little more.
Pool store tests. I did the complete TF-100 test set one morning on a pool sample. I took a second sample to my nearby Leslies. Leslies almost matched every item. They had an additional decimal place in one, and they got CH of 210 compared to my 225. Of course, I can only get 200 or 225, since one "drop" is 25. So Leslies did good water testing--or we both did bad water testing. I buy 12.5% chlorine at that Leslies at a price a bit lower than Walmart. While I'm there I also buy muriatic acid 31.45%. Both of those products come in 1-gallon (U.S.) containers four to a box--easy to stack and store. I also bought a thermometer from Leslies. My wife from time to time makes in impulse purchase of a gadget or float. This particular Leslies also offers a cartridge filter cleaning service, although I've not tried it. And I've bought a couple of miscellaneous parts from them. They never try to sell me anything I don't ask for. I plan now whenever I need chlorine, to do a full TF-100 test and get a second opinion from my local Leslies.
Finally, Shaney, that's one deep swimming pool you have.
