When testing my CYA, I am not 100% sure about when I stop seeing that black spot at the bottom of the tube. I think I saw a link to an example/photo of that test on this site. Can someone please help me to understand this test better? I have wasted a lot of this reagent trying to figure out this reading, and I definitely do not want to add CYA if it is not needed. I have been running my chlorine a little higher than 4, but I did not think it was neccessary to run the SWG for as long as I have been, so I turned it down. My SWG recommends 1-3 FC.
Here are my numbers as of this morning, after a VERY heavy rain last night.
Ph higher than 7.5, but lower than 7.8
CYA 40? 50? 60?