The pitch usually goes something like this: put a mineral cartridge or an ozone unit on the pad and you’ll barely need chlorine. Softer water, no red eyes, no smell. Some of that is true. The “barely need chlorine” part is where it gets slippery, and it’s a question we get a lot when people look at equipment upgrades on our pool services page.

The fair version: these systems are helpers. They can lower how much chlorine a pool needs and make the water more pleasant. They don’t replace the chlorine residual that actually keeps the water safe between pump cycles.

Why chlorine stays in the picture

Chlorine does something none of these systems do: it stays in the water. Every gallon in the pool carries some sanitizer, so germs that arrive on a swimmer get hit wherever they land, not just when they happen to drift past the equipment pad.

CDC’s 2018 summary of its Model Aquatic Health Code, focused on Crypto, says it flatly in the glossary: “A free chlorine residual must be maintained for adequate disinfection.” In that same code, ozone and UV are installed as secondary systems, placed before the point where the primary disinfectant goes in.

For public pools in California, it isn’t optional. Title 22 sets a minimum of 1.0 ppm free chlorine in a public pool regardless of what else is on the equipment pad, and the operator still has to test and log it every day. An HOA that adds UV to cut the chlorine smell still has to hit that number.

UV: kills what passes through the light

A UV system is a chamber on the return line with a lamp inside. Water runs past the lamp, and the UV light damages the germs in that water. When the water leaves the chamber, the UV effect leaves with it.

Pentair’s commercial BioShield UV manual is direct about this. It says the unit “is designed for supplementary disinfection” and “is intended for use with appropriate residual levels of EPA registered disinfecting chemicals.”

The lamp is also a consumable. The manual says a full set of lamps gets replaced after 12,000 hours of use, or sooner if the unit’s UV intensity reading drops below its threshold. A lamp that’s still glowing isn’t necessarily still doing the job.

Where UV earns its place is chloramines, the compounds behind the “chlorine smell” and itchy eyes. Pentair’s residential BioShield page claims a 25% reduction in combined chloramine under its test conditions.

Ozone: strong, fast, and gone

Ozone is a powerful oxidizer generated on site and injected into the plumbing. Like UV, it works on the water flowing through the system, and it doesn’t hang around in the pool as a residual.

It also has to be handled carefully. The CDC code requires ozone systems on public pools to vent and destroy undissolved ozone gas, test the air within 6 inches of the water for less than 0.1 ppm gaseous ozone, and shut the system down automatically if a leak is detected.

On a backyard pool the equipment is smaller and simpler, but the logic is the same: ozone helps oxidize what comes through the pad, and chlorine handles everything else.

What a mineral pool system actually does

“Mineral pool” usually means a cartridge or ionizer that releases silver and copper into the water. Silver is aimed at bacteria, copper at algae.

The EPA-registered label for the Nature2 G45 mineral cartridge is a good example of how these are meant to run. It says the system is used with a chlorine delivery device or “0.5ppm of an EPA registered chlorine pool product.” Start-up calls for 1 to 2 ppm free chlorine, then a “low chlorine recipe” that lets it drift down to 0.5 ppm.

The label also recommends extra shocking after rainstorms or heavy swimmer loads, and tells owners not to use it with copper-based algaecides. Its own troubleshooting chart lists copper as a cause of blue-green stains, which tells you why the metal release is controlled.

Water balance still matters with minerals in the pool. The same label targets pH between 7.4 and 7.8, calcium hardness of 200 to 400 ppm and total alkalinity of 80 to 150 ppm, and says to balance the water before the cartridge goes in.

So a mineral system can cut your chlorine a lot. It doesn’t cut it to zero, and the cartridge gets replaced on a schedule.

Side by side

That last row comes up because people lump salt in with “chemical-free” systems. A salt system is a chlorine system with an onsite generator, which our post on whether a saltwater pool is really less maintenance gets into.

The Crypto problem none of this solves alone

Here’s the honest case for keeping chlorine in range even with all the helpers. CDC says Crypto “can stay alive for more than 7 days, even if pool water is properly disinfected.” Its home pool guidance puts the time for 1 ppm free chlorine to kill it at roughly 10.6 days.

That’s the germ secondary systems are aimed at in public pools, and it’s why the CDC code treats them as an addition to chlorine. Pentair’s commercial UV manual even notes the unit “has not demonstrated an ability to provide three log kill or inactivation of Cryptosporidium.”

The takeaway isn’t that these systems are useless. It’s that they’re one layer, and the chlorine is another.

Is one worth adding to your pool?

It depends on what’s bugging you about the water. If it’s the smell and red eyes, UV or ozone aimed at chloramines can help. If it’s how much chlorine you’re buying, a mineral system can bring that down. If it’s that you want to stop thinking about chemistry, none of them do that.

Any of these goes on the pad as part of the plumbing, alongside the pump, filter and heater, and it adds one more thing to maintain: lamps, cartridges, ozone generators. Before buying, it’s worth reading our post on what actually breaks on pool equipment to see what you’re adding to the list.

If you do add one, the plumbing and electrical changes on the pad are the kind of work covered under our pool equipment upgrades.

Asked at the pad, every week

Can a mineral pool be chlorine free? Not according to the mineral cartridge label we looked at. It still calls for 0.5 ppm chlorine after start-up, plus shocking after storms or heavy use.

Does UV or ozone mean I can skip shocking? They can reduce chloramine buildup, but they don’t replace keeping a chlorine residual. Shock when your readings call for it.

Will a mineral system stain my plaster? The cartridges are designed for controlled copper release, and the label warns against stacking a copper algaecide on top. Keep the water balanced and don’t add extra copper.

Do I still need weekly service? Yes. Your readings should go lower, but somebody still has to test, adjust and check the equipment. Our weekly reports include the water readings, so you can see what the system is doing.

Thinking about adding one?

Tell us what you’re hoping to fix (smell, eyes, chemical cost) and what’s on your equipment pad now through our contact page. We’ll tell you whether UV, ozone or a mineral system fits, or whether better chlorine control solves it for less.

Or call (805) 586-2055. We work on Pentair, Jandy, Zodiac, Hayward and Sta-Rite equipment.