ORP, REDOX, HRR, PPM, TRC, and CYA

by Terence F. O'Neill

How and why did we ever start abbreviating everything and what do all these abbreviations mean? If you are a pool mole, you may recognize some if not all of them.

Our discussion this month is on oxidation of swimmer waste. Ask any pool operator why they are adding chlorine to the pool and most all will puff up their chests and reply,.. "To sanitize the water, to make it safe." While this may be somewhat true, this is not the real reason chlorine is added. The greatest benefit of adding a Halogen (chlorine or bromine) is that these compounds are oxidizers. Read the label on the package.

"CAUTION - STRONG OXIDIZER"

Specifically, oxidation is a chemical change in which electrons are lost. The opposite of this would be Reduction. This is a chemical change where electrons are gained. Confused yet? If not then this will help. Oxidation and Reduction both happen at the same time when an oxidizing agent is added to your pool or spa.

Now we will try to clear this up. Oxidation is obtained by adding chlorine, which is the "Oxidizing Agent". The Oxidizing Agent attacks swimmer waste, which would be the " Reducing Agent". The Oxidizing Agent is stripping away negative electrons from the Reducing Agent. The Oxidizing Agent which is now more negatively charged has been reduced and the Reducing Agent having lost electrons has now become more positively, (or less negatively) charged thus producing Oxidation Reduction.

So how does ORP work? The oxidation-reduction electron transfers are measured in millivolts. A sensing electrode and a reference electrode then read the millivolts.

ORP

The difference in the measurement between the two electrodes is the potential of the oxidizer. The ORP value depends on the oxidation potential of the elements in the water.

Potential is the ability to do the work. What we are really looking for here is how much Potential ( killing power) there is by not measuring the quantity (ppm) of Oxidizing Agent, but the strength of the Oxidizing Agent in the pool and if all works out the way we planned, the chlorine atoms have done their job by Oxidizing the Reducing Agent. Burning up the swimmers waste.

If this is all to confusing and you still have questions, then Terry's home phone number is 610-269-2064. Make sure you call late. He will be glad to answer them on Saturdays or Sundays too.