For your 26000 gallon pool, .8 gallons would raise your free chlorine from 7ppm to 10.1ppm or 3.1ppm. The pool math app is super easy to use, I have the paid version on my phone and take me phone out with me when I check the pool each evening. Besides allowing you to track your levels, it also tracks the weather and you can create logs to keep a permanent record. You can also make your logs shareable so others here can see them. If you hold your cursor over my username, a window will pop up and at the bottom is a blue button named 'Pool Logs'. If you click on that button, you can see the logs for my pool. Very helpful for others to be able to help you. There is also a feature in the app called Effects of Adding. This I what I used to calculate how much chlorine you needed to add to raise your levels 3ppm. You will likely lose around 3ppm of chlorine every day due to the sun, sometimes a little more, sometimes a little less depending on the weather and how much use your pool sees. With a CYA level of 60 (always round up), your target free chlorine (FC) are 7-9ppm.