The sand should last for a long time in some cases years. If you see sand in your pool in probably means it is time to change or if the pool looks cloudy that could mean sand is soft (has lost sharp edges). if you take some in your hands and rub them together it should feel very coarse if not change it
How often should you change the fuel filter?
There is no specific set time that you should change your filter. I would check mine on a weekly basis and if it was dirty I would replace it.
Change the oil filter every time you change the oil.
You should change a furnace filter every 2-4 months.
when it is dirty
Every 30,000 miles.
70,000 miles
The amount of time you run the air conditioner depends on how often you should change the filter. Generally you should change the filter at least once every 5-6 months of use.
Depending on how much you drive your car should be how often you change your air filter. Sources say you should change it when you go to get your oil changed cause they both last about the same time.
The cleaning schedules varies from filter to filter, but a general guideline on any swimming pool filter is to take a reading when the filter is clean, then clean the pool filter when the pressure rises about 10 psi.
Whenever it gets dirty.
every 12000 miles