I now realize I have no idea how big my pool is. We just moved into our house a month ago. We were told that the pool was 25,000 gallons. When I had the pool inspected, I asked the guys who did it if that sounded right, by looking at our pool. They said they thought so. It is a free-form pool, so it is not easy to find the area or volume of the pool. So when I started doing BBB, I used 25,000 as my size in pool calculator. I soon realized that the FC went up higher than expected (but at this point I did not do a FAS/DPD chlorine test to check the exact value). I decided I'd start lowering the size of the pool in pool calculator to see what values seemed to work with my pool, and go with that size. But then I realized that what I thought were stains were mustard algae (the water itself is crystal clear).
So today I started the process to get rid of the mustard algae. I measured my FC at 1.5 ppm, and using pool calculator and 22,000 gallons as my pool size, I figured out I needed 3.8 of the 182 oz jugs of chlorine to reach "standard" shock value of 16. Well, an hour and a half later, I measure the FC and it is 27 ppm . That's even above the mustard algae shock value of 24 ppm I was going to eventually shoot for. I went back into pool calculator, and using all of my measured values for all tests, I played around with the pool size I would have to get a rise from 1.5 ppm to 27 ppm given how much chlorine I added. I came up with between 13,000 and 14,000 gallons. That's a heck of a lot smaller than 25,000 gallons. Perhaps the previous owners meant 15,000 gallon pool size? There is no way for us to contact them anymore. They were already out of state when we bought the house. But shouldn't someone who works around lots of pools be able to tell the difference between a 15,000 gallon pool and a 25,000 gallon pool? Or could something else be causing the discrepancy?
Any advice on how I should proceed from here?