Click on my name, then click on the Pool Math Logs badge. That’s what I use it for as well as determining how much liquid chlorine and muriatic acid I need to add. I find the app well worth the money I paid for it.
It has some functionality without paying, but it is heavily restricted. I wound up paying, figuring that $8 per year (less than $1 per month) was a small price to pay for an app that I use nearly every day to track my pool water parameters. I’m sure there are other apps out there with similar features, and probably some free ones at that, but I don’t think you’ll regret paying for poolmath. If nothing else, think of it as a donation going toward maintaining the app and this website.
I don't have the app yet because my phone is too old and not compatible. But $7.99 for a year seems very reasonable to me. I'm sure the developers worked very hard on it. I've seen screenshots of the app and it looks great. I'm still using the webpage calculator. When I first got my TFT kit, I took it to work and put the case face down on the glass of our copier. I made about 50 copies of the log that's on the TFT kit, put it in a folder and I use it to keep track of my testing. Maybe a bit old school, but it works for now. When I get a better phone, I'd like to try the app.
I have about three years of history now on Pool Math. You can click on my avatar the PoolMath Logs. I find it very helpful for tracking purposes. I could never remember all the details I log there. The notes are especially valuable. For calculations, it does everything the webpage version does but in a nicer format (in my opinion). Free version does all the calculations, including ”effects of adding”. It doesn’t log results though. The specifics of what is included in the free and paid versions are listed out on the app store.