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.