Found out about this website today as I was sheepishly looking for help. I am a drinking water regulator for the state of Washington and thought I could manage my mother in law's first pool for her. Got busy in the field doing inspections and ignored the pool for 4 hot Spokane days and came back to a green pool. I've been reading your threads/posts as fast as I can today so I can get the pool back under control. Getting them set up with better testing equipment and getting them off the pool store chemicals. Thank you all for being here.
Hi Seporah, welcome to TFP!
If you are a drinking water regulator, then you probably know about David Wahman's work about use of chlorinated cyanurates (dichlor and trichlor) for drinking water disinfection, and that it is the HOCl concentration that is relevant for keeping water sanitised. Here some examples of his work:
Since 1958, cyanuric acid and two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid), have been added to outdoor swimming ...
www.ncbi.nlm.nih.gov
Cyanuric acid is present in drinking water when chemicals commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) or trichlor (trichloroisocyanuric acid) are used as alternative free chlorine sources. ...
www.ncbi.nlm.nih.gov
In the United States, approved methods to measure free chlorine concentrations in drinking water systems adding sodium dichloroisocyanurate (dichlor) or trichloroisocyanuric acid (trichlor) as chlorine sources exhibit measurement bias from chlorinated ...
www.ncbi.nlm.nih.gov
The good thing is, that water chemistry doesn't really care whether we want to drink the water or swim in it. TFP's principles are based on the the same chemistry. From reading Wahman's papers, I guess that you might have to get your head around a few differences in what things are called:
Wahmann:
Free Chlorine = HOCl + OH-
Total Chlorine = HOCl + OH- + Chlorinated Cyanurates
Pool Industry:
Free Chlorine (FC) = HOCl + OH- + Chlorinated Cyanurates
Combined Chlorine (CC) = Chloramines
Total Chlorine (TC) = FC + CC
You probably know this already, but I thought I clear that up straight away to avoid misunderstandings.
The pool industry's definition of FC is based on the fact that Chlorinated Cyanurates are showing up in all available Free Chlorine pool test kits. Unfortunately, the Chlorinated Cyanurates are not contributing to killing pathogens in the water. Double unfortunately, wide parts of the Pool Industry ignore this and consider FC and CYA independent parameters.
TFP's recommended
FC/CYA Levels take the percentage of chlorinated cyanurates at a given FC and CYA level into account, and take the ratio FC/CYA as a proxy for the HOCl concentration. Turns out the the FC/CYA ratio is over the pool-relevant range proportional to the HOCl concentration. All the recommended FC levels on our chart are equivalent to each other. These are the tables behind above link:
All the lower ends of the recommended target levels (like FC 5ppm at CYA 40ppm or FC 7 at CYA 60ppm) are in terms og HOCl concentration equivalent to an FC level of about 0.11ppm without CYA at pH 7.5 (without CYA, the pH dependency is quite pronounced (about 50% drop of HOCl between pH 7.5 and 8.0), but CYA buffers this effect and the dependency with CYA in the water is negligible in the pool relevant range (only about 15% effect between pH 7.5 and 8.0)).
The recommended SLAM levels (that you will need to clear your green pool) are equivalent to an FC of about 0.64ppm without CYA.
It sounds like you want to read about the
SLAM Process.