According to the latest working draft of the Model Aquatic Health Code, there’s no reason for indoor pools to use cyanuric acid, even in products such as dichlor and trichlor. The code is still a work in progress, but the decision has some in the industry concerned about the implications of such a restriction.
CYA is used to prevent chlorine from breaking down in the sun, but not all experts agree that there’s enough evidence to restrict its use. The decision by those developing the MAHC to recommend CYA only in outdoor pools was based on review of scientific evidence. Public comments submitted through the MAHC Website will also be considered as the code is finalized.