According to an article on Healthy Water from the CDC, they make a bold statement that “The CDC recommends not using cyanuric acid or chlorine products with cyanuric acid in hot tubs/spas.”
Dichlor is a stabilized chlorine commonly used in hot tubs. The problem is hot tubs don’t need to be stabilized. They are not out in the direct sun all day like pools so they don’t need the UV protection that the cyanuric acid in dichlor offers.
According to J.R. Anderson in his article “A Study of the Influence of Cyanuric Acid on the Bactericidal Effectiveness of Chlorine” it takes 4 times as long to kill common hot tub bacteria when CYA is at 50 ppm and 6 times longer when CYA is 100 ppm.
Multiple sources, including the CDC, recommend eliminating Cyanuric Acid (CYA) from hot tubs. Yet many hot tub owners use chlorine containing CYA resulting in cloudy, smelly water in as little as a few weeks.
Swim Spas are categorized as portable spas. Educational resources listed below apply to both hot tubs and swim spas.
Centers for Disease Control and Prevention (CDC)
CYA: Ally For Pools – Havoc for Hot Tubs
Taylor Technologies stating “Both dichlor and trichlor are over 50% CYA by weight”
National Center for Biotechnology Information Support Center (NCBI)
Pool and Spa News about CYA
Pennsylvania Department of Health