Sand filters need to be backwashed/ cleaned when the water flow in the pool decreases by 30%. If the filter gauge reading has increased 10 PSI over the initial (clean filter) reading it's time to backwash. In other words, if after backwashing the gauge reads around 12 PSI, then you shouldn't backwash again until the gauge is closer to 22. Over backwashing actually causes poor filtration becuase the filter needs to build pressure in order to filter down to a smaller micron.
How To Backwash:
1. Turn off the pump
2. Make sure backwash line is open and water is free to flow out. Set the multiport valve on the backwash position. When moving this handle it's very important to not drag it when switching positions. Fully press down the handle, move in a clockwise position, and drop it on the desired position. There is a gasket underneath that can become damaged if you don't fully press down the handle when moving it.
3. Start the pump back up and backwash until the waste water is clean. Approximately 3-5 minutes. If you have a sight glass on the multiport you can also watch until that runs clear.
4. Turn off the pump. Move the multiport valve to the rinse position.
5. Start the pump back up and rinse for approximately 30 seconds.
6. Turn off the pump. Move the multiport valve to the filter position.
7. Once you restart the pump, take note of the clean filter pressure on the gauge and ensure no water is still coming out of the backwash line. If applicable, open the manual air relief valve until you get all the air out of the filter and a stream of water flows out of the valve.
*Reminder that the sand in your filter should be replaced about every 3-5 years. If you're struggling with clarity and your chemistry is adequate the sand might need to be replaced.*