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What should I know about using ozone to sanitize my pool?

Q: I'm thinking about using ozone to sanitize my pool. What should I know?

A: Good choice! Ozone is an excellent sanitizer that is economical, environmentally friendly, and pleasant for our clients.

Let's start with a basic understanding about how ozone works. You may be surprised to hear that ozone, chlorine, bromine, and peroxide all work essentially the same way - by oxidation. All these sanitizers are common chemical compounds that have an "extra" oxygen molecule. The formula for oxygen gas is O2, while ozone is O3. Plain old salt (sodium chloride) is NaCl, while liquid chlorine (sodium hypochlorite) is NaClO. Water, or H 2 O, becomes hydrogen peroxide, or H 2 O 2 , with an extra oxygen molecule.

These compounds are "volatile" - that is, the extra oxygen molecule makes them unbalanced, and they want to return to the simpler compound. Happily, the extra oxygen molecule is attracted to oxygen-hating bacteria ! So when the two meet, the oxygen molecule detaches from the sanitizer and attaches itself to the bacterium. The bacteria die, and the ozone turns back into oxygen.

Okay - enough about chemistry. Lets talk about your options for adding ozone to your pool.

Because of its extreme volatility, plus the fact that it is a gas, you can't just buy ozone and add it to the water. Instead, you must purchase an ozone "generator", which makes ozone using the oxygen in the air or water. There are two common types of generators: UV light and Corona Discharge (or CD).

In my opinion, you should not even consider a UV generator for a pool, especially one that meets the needs of our furry clients. To generate ozone using UV requires that 1) the water be in contact with the lights for an extended period of time, and 2) there is no "interference" between the UV source and the water. In other words, you have to have a low flow system, you need to have a fairly large chamber with multiple lights, you need to keep the bulbs spotlessly clean, and any kind of cloudiness in the water will interfere with ozone production. In addition, the lights lose effectiveness over time, even before they burn out. In general, UV ozone generators are okay for sanitizing the drinking water in your motor home, but not much else.

CD models are capable of much higher ozone output, AND at a lower operating cost (less electricity, no bulb replacement). They are compatible with higher flow rates and aren't affected by cloudy water. Most ozone generators sold for the pool industry are CD models, but be sure you ask. In a CD ozone generator, room air is filtered and bubbled into the water, which is then passed through electrically charged plates. The electrical charge adds the extra oxygen molecule, and the oxygen in the air is converted to ozone. A similar thing happens during thunder storms, which is why you often smell ozone after a lightning strike.

Hooking up an ozone generator to your pool is fairly straightforward. You'll need to have a small bypass manifold between the filter and heater. Part of the water that is circulating will be diverted into the ozone generator.

Now here's another thing you need to know about ozone and all the other sanitizers as well - in addition to being volatile, they are also corrosive ! Ozone will bleach out color just as chlorine and peroxide will. There can be other reactions: ozone has a tendency to break down silicone, polycarbonates (certain plastics) react to bromine, chlorine destroys latex, etc.

Proper dilution of these sanitizers in water helps to minimize these corrosive effects. However, since it's a gas, ozone is a bit harder to dilute than the others. If you send the ozone gas directly to your pool, you are going to see immediate and serious damage to your pool cover! For this reason, along with your ozone generator, you want to be sure to include a degassing unit, also called an ozone tower.

An ozone tower is basically a tall pipe with an outlet at the top for gas and at the bottom for sanitized water. The water and the ozone mix in the pipe and the bacteria are killed. The gas bubbles (oxygen and unused ozone) are sent out the top (which should be vented to the outdoors), and the sanitized water, minus bubbles, is returned to your pool (not to the heater).

You can purchase ozone towers from most of the manufacturers of ozone generators, and you can also find them at aquarium stores. There are also build-it-yourself instructions for them on the internet. In my opinion, the taller the tower the better.

However wonderful ozone is, it is not usually sufficient as your only sanitizer. Ozone isn't effective against algae. It doesn't remain in the water, so you'll still need a residual sanitizer such as chlorine, bromine, or copper. However, you'll be able to use much lower amounts of the other sanitizers and still keep the water clean and healthy.

Answer courtesy of:

The ACWT Pool Guru:
Karen Hunter
22609 102nd Ave SE
Woodinville , WA 98077
425 487-3078