Cyanuric Acid: The Do's and Don'ts Every Pool Owner Should Know

Cyanuric acid might be the most misunderstood chemical in your pool. Often called chlorine stabiliser or conditioner, it's essential for Australian pools exposed to intense UV radiation – but too much creates serious problems that many pool owners don't recognise until it's too late. Understanding cyanuric acid is crucial because once levels climb too high, there's only one solution: drain water and start fresh.

What Cyanuric Acid Does

Think of cyanuric acid as sunscreen for your chlorine. Australia's powerful UV rays rapidly break down chlorine – within hours on a summer day. Cyanuric acid bonds with chlorine molecules, shielding them from UV degradation and extending their sanitising life by up to 8 times. Without it, you'd burn through chlorine (and money) at an alarming rate.

The Ideal Range

For traditional chlorine pools, aim for 30-50 ppm (parts per million). Salt chlorinator pools run best at 60-80 ppm due to the way they generate chlorine. These ranges provide UV protection without compromising chlorine effectiveness. Below 30 ppm, you'll lose chlorine too quickly to UV. Above 80 ppm, you enter problematic territory.

The Critical Don'ts

DON'T Rely on Stabilised Chlorine Exclusively

This is the number one mistake Australian pool owners make. Trichlor tablets and dichlor granules contain built-in cyanuric acid – about 55-60% by weight. Every time you add stabilised chlorine, you're adding more cyanuric acid. Use these products exclusively, and your levels will climb relentlessly upward. There's no escaping this mathematical certainty.

DON'T Think High Levels Just Mean More Protection

Here's the problem: above 80-100 ppm, cyanuric acid doesn't just protect chlorine from UV – it actually blocks chlorine from sanitising your pool effectively. Your test strips might show adequate chlorine, but the cyanuric acid has essentially locked it away, making it unavailable to kill bacteria and algae. This is called "chlorine lock" or "overstabilisation."

DON'T Expect Chemicals to Lower Cyanuric Acid

No chemical reduces cyanuric acid levels. None. Despite what you might read online or hear at the pool shop, there's no product you can add to lower it. Cyanuric acid is extraordinarily stable – that's literally its purpose. It doesn't evaporate, break down from UV, or get filtered out. It only leaves your pool when water leaves your pool.

DON'T Ignore Creeping Levels

Cyanuric acid accumulates slowly and silently. You might not notice problems for months or even years, then suddenly you're battling persistent algae despite maintaining "proper" chlorine levels. By then, you're likely sitting at 150+ ppm, and your only option is draining.

The Essential Do's

DO Test Cyanuric Acid Regularly

Test at the start of swimming season and monthly during peak usage. Most basic test strips don't measure cyanuric acid – you'll need a specific test kit or strips designed for it. Many pool shops offer free testing that includes cyanuric acid levels.

DO Use Unstabilised Chlorine for Regular Maintenance

Liquid chlorine (sodium hypochlorite) or calcium hypochlorite granules contain zero cyanuric acid. Using these for your regular chlorination prevents cyanuric acid buildup. Add stabiliser separately once or twice per season as needed, rather than continuously through stabilised chlorine products.

DO Consider a Salt Chlorinator

Salt systems generate pure chlorine without adding cyanuric acid. You add stabiliser manually to achieve your target level (60-80 ppm for salt pools), then maintain it there. Salt chlorination is popular in Australia precisely because it gives you control over cyanuric acid levels.

DO Plan for Partial Draining

If levels exceed 80-100 ppm, it's time to dilute. There's no getting around it – you must drain a portion of your pool and refill with fresh water. How much depends on your current level and target level. Use this formula: Percentage to drain = (Current CYA - Target CYA) ÷ Current CYA × 100.

For example, if you're at 150 ppm and want 50 ppm: (150 - 50) ÷ 150 × 100 = 67% drain and refill required.

How to Reduce Cyanuric Acid: The Only Method

Let's be absolutely clear: the only way to reduce cyanuric acid is to physically remove water containing it and replace it with fresh water. Here's how:

Partial Drain Method

Calculate how much water needs replacing using the formula above. Drain that percentage from your pool (measure using tile lines or a marked stick). Refill with fresh water. Retest after 24 hours of circulation and adjust if needed. This is the standard approach for moderately high levels (80-150 ppm).

Complete Drain Method

For dangerously high levels (200+ ppm) or if you're due for other maintenance requiring an empty pool, drain completely. Never drain a pool yourself without professional advice – empty pools can "pop" out of the ground from groundwater pressure, crack from soil movement, or suffer structural damage. This is particularly risky in Australian clay soils that expand and contract with moisture.

Backwashing and Splash-Out

Regular backwashing removes small amounts of water (and cyanuric acid), as does splash-out from swimming. These help slow accumulation but won't significantly reduce high levels. Don't rely on them as a correction method – they're just modest preventative measures.

Australian-Specific Considerations

Our intense UV means stabiliser is non-negotiable – you need it. However, our long swimming season (6-9 months in most regions) means continuous chlorine use and rapid stabiliser buildup if you're using the wrong products. Perth, Brisbane, and northern Australia face year-round swimming conditions, making stabiliser management even more critical.

Water restrictions in many Australian areas make draining pools problematic or expensive. This is another reason to prevent high cyanuric acid rather than correcting it – you can't always afford the water to fix the problem.

Recognising Overstabilisation Problems

Your pool might be overstabilised if you experience:

• Persistent algae despite maintaining chlorine levels
• Difficulty keeping chlorine readings stable
• Cloudy water that doesn't respond to shocking
• Excessive chlorine demand – constantly adding more
• Test strips showing adequate chlorine but pool looks poor
• Inability to achieve effective shock chlorination

Prevention Strategy

The best approach is preventing high cyanuric acid in the first place:

• Use liquid chlorine or cal-hypo for daily sanitising
• Reserve stabilised chlorine (trichlor/dichlor) for occasional use only
• Add pure cyanuric acid granules once or twice annually as needed
• Test cyanuric acid monthly during swimming season
• Factor in partial draining every 2-3 years as routine maintenance
• Keep detailed records of cyanuric acid levels and trends
• Consider salt chlorination for easier stabiliser management

Fun Fact: Cyanuric acid is so stable that if you added 50 ppm to your pool and never added another drop of stabilised chlorine, that same cyanuric acid would still be protecting your chlorine 10+ years later! It literally lasts decades unless you physically remove it through water drainage. This remarkable stability is exactly why it's such an effective UV protectant – and exactly why managing it requires careful attention. Once it's in your pool, it's staying there.

The Bottom Line

Cyanuric acid is your chlorine's best friend in Australia's harsh sun, but like many good things, too much causes problems. The golden rule is simple: use unstabilised chlorine for regular maintenance and add stabiliser separately only when needed. Test regularly, and don't let levels creep above 80 ppm.

Remember, there are no shortcuts, chemicals, or tricks to reduce cyanuric acid except draining water. Prevention through smart chemical choices is infinitely easier than correction. Understand what you're adding to your pool, test regularly, and maintain appropriate levels. Your pool – and your wallet – will thank you for avoiding the expensive, water-wasting hassle of corrective draining.

If you're already facing high cyanuric acid levels, accept that dilution is your only path forward. Calculate what's needed, plan your drainage, and start fresh. It's the reset your pool needs to function properly again.