Filters can last from a few weeks to several years. It depends on the materials they were made from, and their anticipated life expectancy. As a general rule, most cartridge filters average 1 year. It is recommended that you clean your spa filters every 30 days to extend filter life. You need to clean them with chemical products to remove the oils etc. In between cleanings just spray them off with the water hose. A good clean and soak with our Dazzle Filter Cleanse will help remove oils and scum from the filter media. If you do not use the Filter Cleaner & Degreaser, and the pH of the water drops significantly, it can make the oils embed into the filter permanently. This will make your pump(s) work harder, and take longer for the water to clear. It also reduces ripping, extending the life of a filter. Even potentially doubling filter life.
As far as when to replace a filter, there are few indicators that may be helpful. To a degree, you can look at the filter, and if it looks nasty even after a good cleaning, it may be time for a new one. Discoloration, folds starting to stick together, calcium or chemical buildup that cannot be dissolved easily, and visible tears are just a few common indicators of needing a new filter. Also, if the water tends to stay cloudy after a long filter cycle and is chemically balanced, this may indicate poor filtration. If your heater keeps shutting off, pull the filters out to allow the tub to run if the heater stays on this is a REALLY good indication of dirty/bad filtration. Lastly, if your pump/motor starts to run a little louder then normal, try pulling the filters. If the noise lessens, it’s a good indicator of needing new filters.
If it gets to the point where the heater is shutting off and/or the pump is making noise, this is often too late. Your heater and/or pump may be damaged from this flow restriction.
Keep up on chemically cleaning your filters, and replace them at least every other year.
Preventative maintenance is the key to proper water and equipment care.