Throughout the book and course we'll use chemical and technical terminology as infrequently as possible. That's probably not infrequently enough, because there's been concern expressed (that means complaints) over the number of technical words required. You're going to be a professional AFO, right? So sound like one and begin using these terms.

Units, all those increments of measure, are necessary when discussing water conditions and treatment. They are most often abbreviated. Let's explain just one now; the rest will show up in the text or in the course and be either self explanatory or explained on the spot. If you're confused, stop the show and ask!

"Parts per million" is a very common term, abbreviated ppm. It's also confusing to newcomers. Unlike specific units of measure-like pounds, meters, or volts – a ppm is a comparison (or ratio) of the quantity of a diluted material as compared to the whole volume of liquid in which it is diluted, using the same unit of measure. Still confused? Don't panic; check these examples first…

To illustrate: One part per million of chlorine is a pound of chlorine in a million pounds (not gallons) of water. And you don't need to actually have a million pounds – that's why they use the word "part." It could be a pint in a million pints or even a drop in a million drops, or an ounce in a million ounces. The only rule is that units of measure have to be the same. And the stuff you're comparing must be full strength, or adjusted for its dilution. You can't pour a gallon of whiskey in a million gallon pool and call it a part per million alcohol. You gotta' figure the percentage of alcohol in the booze, maybe 50%. In this case, you'd only have half a ppm alcohol in the pool – still a waste of good hooch and a pretty silly example…

Prep School Basics :: Pool-Water Chemistry Made Simple