TDS (Total Dissolved Solids) is a measurement of a variety of solids that are dissolved in your hot tub (or pool) water. As a general rule, hot tub and pool water is recommended to be maintained at levels of less than 1500 ppm of TDS. The exception to this is hot tubs treated with salt (Salt water sanitizers*). If a hot tub is utilizing a saline system then the amount of salt present in the water will be detected with a TDS test. The amount of salt in a saline hot tub could be between 1250 to 5000 ppm, it is therefore important to first determine the ppm of the salt and then subtract that from the TDS number. The normal way to reduce the TDS is to drain the hot tub and refill.
CYA (cyanuric acid) or stabilizer is found in stabilized chlorine products, used in hot tubs for sanitation. In swimming pools CYA is helpful in preventing loss of active chlorine being consumed by sunlight. In a hot tub it has no function, but is part of the product. The recommended levels of CYA in a hot tub are less than 60ppm. At levels above this is could interfere with the effectiveness of the chlorine. It is rare to see CYA levels in a hot tub exceed 60ppm because it is only added through the use of the sanitizer and it is one of the components of TDS and is usually reduced or removed as part of a spas regular drain and fill routine.
Occasionally the CYA levels in a hot tub can climb to extreme levels even when the TDS is being monitored. This normally occurs when the spa owner only drains a portion of the spa's water and "tops" the tub up. The Hot tub owner has reduced the TDS and removed some of the CYA but both levels will now be starting from a higher level and the CYA will slowly become a greater portion of the TDS.
To avoid high CYA levels it is recommended that hot tub water is completely drain 1 to 3 times a year (whether using stabilized chlorine or bromine, and depending on usage- consult with your hot tub professional). If you suspect you have an elevated CYA level, ask your water care tech to do a CYA test, when next you have your water tested.
*in Canada ALL salt/saline systems MUST have a Health Canada registration number.
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