How does cyanuric acid affect chlorine efficiency?

by brittney_cutler_2 | June 28, 2022 8:00 am

[1]

Balancing cyanuric acid levels for safer pool water

By Kevin Vlietstra

Pool water needs chlorine to keep it safe for bathers. It is added primarily as a sanitizer, but it can also act as the primary oxidizer of waste and prevent algae from multiplying. When there is plenty of chlorine available, it can be used to do all three jobs. But, when it is in shorter supply, other supplements can be added to decrease the overall amount of chlorine needed, or to extend the longevity of the existing chlorine.

Cyanuric acid (CYA) is commonly used as an additive to stabilize, protect, and conserve chlorine in its tablet and liquid forms. This article will focus primarily on the role of CYA to help conserve chlorine, as well as how it affects water quality as it accumulates in the pool.

What does CYA do and how is it added to pool water?

When discussing chlorine and CYA, it is important to summarize the two types of chlorine for water treatment: chlorine with stabilizers and chlorine without stabilizers. Chlorines without stabilizers are sodium hypochlorite (liquid chlorine bleach) and calcium hypochlorite (often abbreviated as cal-hypo). Chlorines with stabilizers are usually referred to as ‘trichlor’ or ‘dichlor.’ The full names of these products are reflective of how they are created. For example, trichloroisocyanuric acid (trichlor) is created from reacting ingredients with CYA to create a granular chlorine concentrate.

[2]

The moment dichlor or trichlor is applied to new water, CYA is introduced. The stabilized chlorine will also produce hypochlorous acid (HOCl), which will bond with the CYA. As a result, the HOCl will last longer when the pool is outdoors and ultraviolet light shines down on it. At the first part per million (ppm), chlorine is retained in the water longer than without CYA. Once the presence of CYA reaches around 25 ppm, a greater amount of chlorine (HOCl) is protected against loss in the presence of ultraviolet light.¹ When chlorine stays in the water, both time and money are saved for the pool owner.

Using chlorinating compounds with stabilizer will continuously add CYA to the pool. However, once CYA levels reach 50 ppm, the benefits of chlorine retention start to level off. Looking ahead to higher levels, such as 100 ppm, there are no significant benefits to having more CYA in the water[3].

From a closer perspective, hypochlorite ions (OCl-) are formed with HOCl when chlorine enters the pool. When the pH is low, more HOCl is available at the time of chlorine addition. The opposite is true when the pH is higher. Another factor in HOCl availability is the presence of CYA. When CYA is present, even at the first ppm, it has an immediate negative impact on the dissociation of HOCl and OCl-. Adding more CYA will increase this impact. This is likely one of the reasons using CYA is not recommended in commercial pools.

Can there be too much CYA?

[4]

Manufacturers and standards organizations have set the reference level of too much CYA at 100 ppm. This is a good rule of thumb, as it helps keep information uniform between service staff and sets a residual for pools which may have a history with water quality or algae growth issues. However, the decision to maintain higher CYA levels ultimately comes back to the pool owner.

To determine the severity of elevated CYA in a particular pool, it is important for the service professional to discuss the matter with the owner and decide whether to take immediate or future action. The main concern is the conditions in which chlorine may be consumed in the water. How often the pool is used is a key piece of information, as more pool use equals more chlorine use. One should also assess the area around the pool and the property, to find out if it is prone to windy conditions or has significant (or limited) outside plant life.

Pools with continuous circulation systems could also have CYA levels above 100 ppm. In these situations, if they are limited in one element and especially in all elements, then higher CYA levels could have limited impact on water quality or safety. However, the owner will need to be advised that if any of these conditions change, the water’s ability to correct any upsets may pose a challenge.

Pool water should always be safe water. As long as a free chlorine residual can be maintained above one ppm, CYA does not greatly hinder HOCl’s ability to inactivate or kill common germs and bacteria. The rate of sanitation and inactivation will decline, but if there is still free chlorine present, there is still the potential to help keep the water safe[5].

Unfortunately, the elevated presence of CYA does reduce the oxidizing ability of chlorine. Once CYA is added to the water, the millivolt (mV) levels immediately start to decline, reducing the chlorine’s efficacy in disinfecting the pool[6]. For instance, 75 ppm of CYA can lower its oxidation reduction potential (ORP) to around 185 mV[7]. Fortunately, if CYA levels continue to increase, especially over the 100-ppm threshold, the rate at which the ORP declines levels off. Since less germs and bacteria would be removed in the presence of elevated CYA, more chlorine (or another oxidizer) would need to be added more frequently, to reduce waste buildup and prevent common water issues.

In the presence of elevated CYA levels, there are several options which can aid in keeping water clean and clear. Simply raising the chlorine level is one solution. Maintaining a free chlorine level of 7.5 per cent of the total CYA levels is a popular methodology. Another option would be to use alternative oxidizers, such as potassium monopersulfate, to address water contamination. These oxidizers do not bond with CYA like HOCl does, so the ORP would not decrease.

The water can also be treated with additives which do not include oxidizers. Enzymes offer optimal maintenance relief, as they help break down complicated molecular structures which may otherwise prevent chlorine from effectively doing its job. Borate products can help with water clarity, algae suppression, and sustained water balance. Maintaining reduced phosphate levels can offer relief in the case of reduced chlorine levels. Keeping filters free from grease and oily deposits with dedicated cleaning solutions can also help reduce reliance on chlorine. Lastly, algaecides can help reduce algae presence.

How can CYA levels be reduced?

Currently, there are not many options available to reliably reduce CYA. Chemical treatments do exist, but strict adherence to the directions may pose challenges to the applicator. Using a portable reverse osmosis system (OS) works but requires several days and these treatment systems are not widely available. A popular service trick, which is said to reduce CYA more reliably, is to let the water settle for several days. Then, it must be vacated from the bottom of the pool using a submersible pump. Aluminum sulfate may also help reduce CYA[8]. Regardless of how the water is removed, it will need to be replaced with fresh water to properly correct the issue.

Author

Kevin Vlietstra is the technical director and regulatory specialist with Haviland Pool and Spa Products. He has been working in the recreational water industry for more than 20 years. Vlietstra can be reached via email at kevinv@havilandusa.com.

Source URL: https://www.poolspamarketing.com/trade/features/how-does-cyanuric-acid-affect-chlorine-efficiency/

---