OK -- tonight, add a gallon of 10%. Let the pump run for 45 minutes or so, and test the FC. Record that. In the morning, before the sun hits the pool surface, take a sample and test the FC. See what FC drop you get over night. That is what is called a Overnight Chlorine Loss Test
OK -- the 'about' is not great when it comes to testing. But sounds like you did not lose any overnight. But there is no way that chlorine is full strength as each gallon should add just over 4 ppm FC. And it does not sound like it is.
Hello. So after being gone for a few days, and leaving a few tabs in a floater, i find the pool looking okay, but in need of brushing. I do the brushing, add 10% Home Depot liq chlorine, and run the pump for an hour. Then i test. It's at 3ppm. Does this still look like a case of weak chlorine, or am i overlooking something or doing something else wrong?