Two of the common types of chlorine used in swimming pools is trichlor and dichlor. Both types of chlorine include cyanuric acid (stabilizer) which is used to protect the chlorine from the suns ultraviolet light. Why would you want cyanuric acid in your spa? If your spa isn’t covered and the sunlight hits it then OK. If you use tri-chlor in your pool, and you have a separate spa you may out of convenience use it for both. But, when you use trichlor, the chlorine will soon be gone, but not the cyanuric acid. You will keep adding more trichlor or dichlor over the months, ever increasing the cynuric acid concentration in your spa. We have converted many spas and above ground pools to saltwater chlorine generators and the cyanuric acid concentration was well over 100 PPM. Cyanuric acid doesn’t go away and since pools have such a large water volume the concentration added is small, but in a spa that isn’t the case.
High cyanuric acid levels will reduce the chlorine efficiency and contribute to high total dissolved solids. It may take chlorine longer to kill bacteria and other microorganisms introduced to the water. It may be necessary to drain and refill with fresh water in order to lower the level. Local health authorities often require swimming pools to be maintained under 100 ppm. Cyanuric acid levels in pools should not exceed 150 ppm.