Ozone can provide an effective supplementary disinfection system for swimming pools.
This naturally occurring gas, which is composed of three oxygen
atoms, is one of the most powerful oxidizers known to man —
25 to 200 times faster at killing algae and bacteria than
hypochlorous acid, the strongest form of chlorine.
And because ozone attacks organisms by ripping through their cell
walls instead of disrupting their metabolisms from the inside,
it’s lethal not only to bacteria and algae, but also to
viruses, and even microbes such as cryptosporidium and
Isolating an ozonator performance issue can involve a bit more
detective work than, say, adjusting pH or total alkalinity. Here,
we’ll examine a variety of possible ozonator issues, and walk
through the solution process step by step.
Demand and consumption
At the outset of a service call, it may not be immediately clear
whether the sanitation problem lies with the ozonator itself, or
elsewhere in the system.
Perhaps the simplest test is a visual inspection of the
water’s clarity. A properly functioning ozonator does more
than just sanitize and oxidize — the ozone it produces reacts
with organic and inorganic particles in the water, causing them to
flocculate (clump together) for enhanced filtration. Thus, if you
notice cloudiness in the water — and the pool’s filter
is functioning properly — this is likely a sign of ozonator
troubles, because it can point to an absence of flocculation.
But even if the water’s clear, a test of chlorine residual is
a worthwhile starting point for diagnosing a sanitation problem.
Ozone’s chemical structure breaks down quickly in water
— depending on the level of contaminants, it takes anywhere
from a few seconds to several minutes. Thus, it’s impractical
to maintain a long-term ozone residual in the pool.
“You can’t build an oxidizer residual with
ozone,” explains Roy Reed, owner of Memphis Pool in Memphis,
Tenn., “so you’ve got to maintain a little residual
[with other chemicals] to keep up with that sanitizer
demand.” This means a 0.5-1.0 ppm residual of a halogen
oxidizer — usually chlorine — is necessary to ensure
that all contaminants in the pool are steadily oxidized.
Test the water’s chlorine level, and check for proper
sanitizer levels in the pool. Alternatively, if the pool is using a
commercial-grade ozone system, it may include a built-in oxidation
reduction potential (ORP) meter, which makes it possible to check
the water’s ability to oxidize contaminants. The ozone system
may be experiencing problems if one of three conditions are
present: The water’s chlorine residual is lower than normal;
a higher-than-usual amount of chlorine has been needed to meet the
pool’s chlorine demand; or the water’s ORP reading is
lower than normal.
Before proceeding to the ozone generator, it’s important to
check for some other common reasons the pool’s chlorine
consumption may have gone up. Check to see if debris such as leaves
or dirt has been falling into the pool. If it’s rained
recently, ask your customer if the pool was left uncovered during
the storm. It’s also worth finding out if the homeowner threw
a pool party recently, or knows of any other conditions —
such as landscaping or water-loving pets — that might have
contributed to a spike in chlorine demand.
Addressing conditions like these is crucial, because even if the
ozone generator is working properly, the pool’s chlorine
demand may still need to be recalculated, and the oxidizer output
“Having an ozonator doesn’t negate the necessity of
maintaining a proper chemical balance in the water,” Reed
Pipes and valves
Once the nature of the sanitizer issue has been determined, the
next step is to begin tracing the trouble to its source. If a
problem with the ozonator is suspected, it’s helpful to start
by inspecting the ozone generation system for any obvious signs of
damage, like a frayed power cord or broken electrical connection.
If any major degradation is present, it may be necessary to replace
that portion of the system’s electrical wiring.
Next, inspect all check valves within the ozone system for water
leaks or blockages. If any are damaged, they’ll need to be
replaced right away — a broken valve not only prevents proper
ozone circulation, but it may also allow water to flow into the
ozone generator, causing additional long-term damage.
Some professionals recommend using multiple “layers” of
check valves to ensure a minimum likelihood of leakage.
“Create redundancy with your check valves, so you don’t
have to constantly watch them,” says Steve Stubbs, principal
of Riviera Pools and Spas in Los Angeles. “Make sure that
there are at least two check valves in line before the [ozone]
generator pack, and always carry some extras in your truck. From a
mechanical standpoint, those valves are the places that are most
likely to fail first.”
Another potential trouble spot is insufficient suction of ozone
gas, often caused by an improper pressure differential across the
ozone generator’s injector (sometimes called a venturi). The
pressure on the inlet side of the injector must be higher than the
pressure on the outlet side to ensure sufficient suction and proper
“Make sure there is a presence of vacuum at all times —
even when servicing the system,” Stubbs says, “so that
you’ve always got something pulling the gas through the
Some generators include pressure gauges on both sides of the
injector, while for others, you’ll need to check the
performance of the injector by using an air flow meter at the
injector’s gas inlet port. Regardless of which method is used
to check air flow, any necessary changes can be made by adjusting
the injector bypass valve.
Manufacturers typically provide a pressure differential
recommendation for optimum suction performance on each model they
make. If someone’s noted operating parameters such as this on
a previous visit, it pays to check that the current settings are in
line with the values observed when the system was last working
properly — and to note any settings changed on this visit.
“That way,” Stubbs says, “the next time you see
something awry, you have a starting point for ascertaining
what’s gone wrong.”
Into the system
No matter what is determined about the pool’s chlorine demand
and the generator’s plumbing conditions, it’s generally
worthwhile to run a few checks on the ozonator itself. Many ozone
systems include an indicator light that reflects proper operation.
If the light is on, the problem likely lies somewhere in the
plumbing, or with the water’s chemistry. Conversely, if the
light is off, or showing a different color than usual, the ozone
generator is probably experiencing a problem.
The next step is to determine whether the system is an ultraviolet
(UV) or corona discharge (CD) ozone generator, because each type
entails its own unique setup, and its own problem-solving
methodology. Both types of ozonators are popular in residential
applications, and meet the supplementary sanitizer demands of a
Within a UV ozonator, the only part that’s necessary to
inspect is the UV lamp. If the lamp isn’t lit, try replacing
the bulb or checking the electrical wiring. If the lamp is lit, the
next step is to determine whether it’s producing ozone. This
can be done with an ozone test kit, which is available from a
variety of ozone and test kit manufacturers.
CD ozone systems are available in residential and commercial sizes,
but many residential pools also use commercial-grade CD ozone
generators. “I usually put commercial ozonators on my
residential applications,” says Steve Kenney, owner of SRK
Pools in East Hampton, N.Y. “I’ve found that
residential units just don’t meet the oxidizer demand we see
up here in the Northeast.”
Commercial-grade CD systems involve more complexity than UV or
residential CD ozone generators, but any issues can typically be
isolated to one of a few key areas.
If the CD system uses an air dryer, check the moisture level around
it using a dew point monitor. Even a small amount of moisture
accumulation can foul the dryer and interfere with ozone
The process of corona discharge causes some chemical reactions with
other molecules in natural air — most notably hydrogen (H)
and nitrogen (N), which react with the free oxygen atoms (O) to
form nitric acid (HNO3). Thus, if the system isn’t
using an oxygen concentrator, it’s important to check for
nitric acid buildup in the ozone cell or downstream plumbing. If
the buildup is severe enough to create a blockage or otherwise
inhibit the ozonator’s normal operation, it’ll be
necessary to determine whether the part in question can be cleaned,
or if it needs to be replaced.
However, most commercial CD ozone generators — including many
installed on residential pools — use an oxygen concentrator
to draw pure oxygen from the air, allowing for a much purer and
more concentrated ozone output. If the system includes an oxygen
concentrator, check to make sure there’s a clean air filter
in the concentrator’s compressor, and check with an oxygen
meter to determine the concentrator’s exact oxygen output. If
the compressor hasn’t been serviced within the past year, or
if you notice any abnormal air flow or unusually high oxygen
pressure, the air filter — or perhaps the entire compressor
— will need to be replaced.
Determining the pool’s sanitizer demand, checking the
mechanics of the ozonator’s plumbing, and verifying its ozone
production are all significant factors in any informed decision
about the system’s needs.
“All of these elements contribute to the synergy required to
maintain the level of sanitation required by a specific body of
water,” Reed says. “At the end of the day, the
effectiveness of the ozone process depends on an operator’s
trained eye, and careful monitoring of all aspects of the