Our chlorine generators should last between 7000 and 10000 hours of chlorine production. As they approach and exceed 7000 hours, you may notice that the chlorine production is dropping and you are increasing the power levels to keep the chlorine in range. This may also be more noticeable if when you installed your spa chlorinator you started with fresh water.
If you are not close to the life span then there may be a buildup of organic material and phosphates in the hot tub water which has increased the chlorine demand of your spa. The chlorine demand of your spa is simply the chlorine that is consumed by your spa and the saltwater system must make more than this amount for the chlorine to increase and be measured. Increasing the water temperature increases the demand as well as organic material, phosphates, amount of time since water replacement and so on.
Replace the water if over 8 months old.
Shock the spa water with either a chlorine free or if you don’t mind adding chlorine a chlorine based shock.
Other things to try are phosphate removers, enzymes and make sure your ozone generator is working if you have one.