As the pool season winds down here in NY, I have been primarily taking care of hot tubs for the past few weeks. I've been paying close attention to test results for "Free Chlorine" and "Total Chlorine", and I've started to notice some trends that I didn't realize were there until recently.
A while back, I learned about Bromine pools/tubs. My understanding is that Bromine does the sanitizing, but converts to Bromide as it is consumed. When it runs out, we add an oxidizer that will turn the Bromide back into Bromine. The oxidizer is consumed in the process. So I started thinking and realized I don't fully understand what the Oxidizer is doing.
My relatively new understanding of Bromine made me realize that there is no need to regularly add Bromine tablets to a tub. Once the Bromine is there, it simply needs to be re-activated with an oxidizer. I use MPS as an oxidizer, and if I test the water immediately after adding it, I will see high "Total Chlorine" and usually no "Free Chlorine". After about 5 minutes, the test will show the presence of higher "Free Chlorine". I interpret this to be the re-activation process of Bromine I just described.
So what does this all have to do with the title of my post? I've been referring to the tests as "Free Chlorine" and "Total Chlorine" even though I'm dealing with Bromine. The test is the same test for Chlorine as it is for Bromine as it is for MPS (MPS shows up as Total Chlorine"). So the test isn't really telling me how much Chlorine is present. For that matter its not telling me how much Bromine or MPS either. I suspect it is measuring something like Oxidation Potential. To be clear, I'm referring to the tests used in Test Strips. I'm not sure if they work on the same principles as the liquid tests. So what are they actually measuring that we interpret as "Free Chlorine" and "Total Chlorine"?