Double checking pool volume

[linuxninja00]

When I inherited our pool a few years ago I found some paperwork from the previous owner that stated 30k gallons. I also measured and punched the data into the volume calculator and ended up around 30k as well. Our pool is vinyl with a 8ft deep end and 4ft shallow, but it slopes down as well as the sides slope down in the deep end rather than straight down. I imagine that's typical for vinyl, but I wonder if those slopes are cutting out more volumes than I thought. Lately I've noticed that I'm overshooting my chemical goals with certain tests, like FC. This makes me think the pool is smaller than I believe. If I use the PoolMath app to estimate "Effects of adding X" then see if that amount matches reality when I add said chemical, is that a good way to double check? I know tests like salt have a large +/- so maybe that isn't the most accurate, and I would guess same with CYA. However is FC with bleach a more accurate chemical to test with that has a smaller margin of error?

 

[mknauss]

You can use bleach - though depending on what you are using the concentration can vary. Probably the most reliable is muriatic acid. Do you add that ever? If so, say you want to drop from 8 to 7.6 pH. Add what PoolMath says. Circulate water for 30 minutes and test pH. If different than 7.6, adjust the pool volume in your first calculation until PoolMath shows the actual pH you got based on the amount of acid you added. Also reliable is increasing TA with baking soda.

 

[Richard320]

You have things figured out.

After I kept undershooting on everything, I raised the volume in poolmath and tried again. I got lucky; I only had to up the volume twice by 500 gallons until things behaved the way they were supposed to. For me, it was the acid versus the TA drop that proved to be the most dependable way to verify things. But I had TA up close to 200, so it was easy.

 

[linuxninja00]

Thanks both Marty and Richard. I do add acid on occasion since I'm running SWCG, it drifts..... usually slowly. Since I have all my logs in the pool I think we can dial this in with the TA. I started the season with a TA of 40. According to my logs I've added 12lbs of baking soda and 8lbs of borax (20 mule). I'm sitting at 80 TA right now. If i tweak the size of my pool in PoolMath to 25k, PoolMath states that the baking soda and borax should have raised my TA 44ppm. I think that can help me dial it in, thanks!