As the Model Aquatic Health Code (MAHC) undergoes its third revision, for the fourth edition, the issue of cyanuric acid remains top of mind.

Three years ago, the Council for the Model Aquatic Health Code (CMAHC), which oversees the revision process for the code, devoted a committee to this very issue. In 2019, the Cyanurate Ad Hoc Committee garnered attention when it proposed that CYA levels be regulated based on their ratio to chlorine levels, as opposed to a straight parts-per-million reading. More importantly, the group wanted the ratio to be limited to 20:1. That more than cuts in half the defacto ratio of 45:1 that occurs when CYA is limited to 90 parts per million (the maximum allowed in the MAHC) and a chlorine residual is maintained at 2 ppm (the MAHC minimum).

For this year’s revision, the committee sought to gain more consensus and has filed a new proposal. However, certain members have filed opposing suggestions. The group also came together and proposed other related changes.

Delving deeper

Last year, the Cyanurate Ad Hoc Committee had detractors from the 20:1 ratio among its own members. The proposal could not be submitted under the committee’s name, since members who produce chlorinated isocyanurates would not be associated with it. Instead, the individuals who agreed with the ratio placed their names on the paper.

In January, the committee members submitted the 20:1 ratio as a proposed alteration to the code, known as a change request, to be voted on by the CMAHC at large. But then the group reconvened and explored the issue further, addressing some objections that had been expressed about the methodology behind the 20:1 ratio. Certain assumptions had been factored into the calculation of the ratio. For instance, the calculation assumed that pools would be used 24 hours a day, with no recovery time for sanitizers to restore water quality. Having received strong negative responses to that assumption, the committee re-evaluated and changed it to reflect a 6-hour turnover rate.

Some also took issue with the high bather loads of 15 square-foot-per-person that were factored in. The group adjusted that to reflect the MAHC, which specifies 15 square feet per bather in agitated water and 20 square feet in flat water.

The committee addressed a handful of these fine-tuning issues in the hopes of reaching consensus among all members, including those representing makers of both chlorinated isocyanurates and calcium hypochlorite. However, after replacing some existing data in the model with newer material they considered more appropriate, the committee still fell into two camps — one that wanted the 20:1 ratio, and the other that preferred the defacto 45:1 ratio. However, some data combinations also suggested a ratio of 30:1 was appropriate.

In a vote, the group chose the latter option. While complete consensus wasn’t accomplished, the committee reached enough agreement that isocyanurate specialists were willing to place their names on the paper as part of the committee, with a footnote saying that the group did not reach complete consensus.

“It wasn’t unanimous, but it was somewhat of a balance between risk reduction and operational impact,” says Richard Falk, a member of the ad hoc committee and founder of WaterGuru, based in Menlo Park, Calif.

The group officially submitted the ratio as a change request.

Other Proposals

The committee submitted another two changes meant to serve as a package deal with the 30:1 ratio.

One would raise the CYA maximum to 180 from the current 90, provided the test methods used can measure CYA concentrations as high as 200 when a 2-to-1 dilution is used. The CYA level also would have to fall within the 30:1 ratio. This would not be practical in localities that enforce the Environmental Protection Agency’s limit of 4 ppm of chlorine. In those cases, if observing the 30:1 CYA-to-chlorine ratio, the CYA would have to cap off at 120 ppm. But few jurisdictions require adherence to the EPA limit, Falk said.

The committee also submitted a change request that would require the closure of public pools that fail to maintain certain disinfectant benchmarks: free chlorine concentrations of 1 ppm or higher; CYA:free chlorine ratios of 45:1 or below; spas with free chlorine concentrations of 3 ppm or higher; and brominated pools and spas that don’t meet minimums currently in the standard. It also would call for closure if CYA concentrations rose above 300 ppm.

Combined, these proposals are intended to minimize the operational impact of the CYA:chlorine ratio.

Opposing views

On their own, certain members of the ad hoc committee submitted their own change requests regarding the CYA ratio.

A representative from a cal hypo manufacturer proposes changing the ratio to 15:1, while the CMAHC’s Isocyanurate Industry Ad-Hoc Committee proposes a 50:1 ratio. Another would require that all aquatic venues maintain a free chlorine level of at least 1 ppm, regardless of CYA. Currently, that requirement only applies to pools with CYA present.