How to Backwash Your Media Filter
What is backwashing?
Backwashing is a routine maintenance task required for media filters. It’s easy and quick to do and is necessary to ensure your pool stays clear and your equipment & your filter are operating optimally.
If you don’t backwash regularly you will experience high pressure in your filter putting pressure on seals and fittings and reduced water flow which leads to poor filtration (cloudy water) and potentially poor performance of other equipment such as suction cleaners and salt water chlorinators. Poor water flow can also cause ‘low flow’ warnings and sometimes your system will switch off to protect your pump.
Purpose
Backwashing is how you clean your media filter (sand or glass). It works by pushing the water backwards through the filter, releasing the contaminants the filter has removed from your pool and flushing them and the resulting dirty water down the waste pipe.
Though media filters can look different, the vast majority function the same way and the following process will be applicable to almost every media filter you might have.
Left image shows water traveling down through the multiport valve through the media and back to the pool via the laterals at the bottom. The right image shows the water flow is reversed for backwashing pushing up from the bottom and stirring up the media.
How often?
Frequency of backwashing is dependent on a lot of factors, including how often the pool is used, the environment the pool is in (ie if it’s surrounded by trees or if you live on a dirt road and have a lot of dust enter the pool).
Pressure is the best indicator of when to do a backwash. Most manufacturers suggest you only need to backwash once the pressure has reached 50kpa or more above the ‘original starting pressure’ when the filter was first installed or the media was changed. However, most people don’t know what that is and this doesn’t take into account other equipment on your system that may be affected by lower water flow.
We suggest you backwash once a month as a routine or if the pressure increases by more than 15-20kpa above your normal operating pressure.
That way you ensure optimal water flow ensuring your pool is adequately filtered and other components of your system also operate correctly.
How to backwash your filter
Before commencing a backwash, ensure you have enough water in your pool. For most pools we would expect to use only 500 litres of water but backwashing will lower the water level so you might need to fill your pool higher than normal before you start.
1. If you remember run your pump to check the pressure on the gauge before you start then Turn off the filter pump (never move any valve without ensuring the pump is switched off first to avoid damage due to drastic pressure changes).
2. Push down on the multiport valve handle then rotate it to change from “FILTER” to “BACKWASH” See photo of the two most common styles of muliport valves.
See photo of the two most common styles of muliport valves.
3. If your filter is old you may have an additional valve fitted on the waste line, if so you will need to open it first.
IMAGE OF FILTER WITH VALVE?
4. Turn the filter pump back on to begin the backwash
5. Look at the “sight glass”, you should see water flowing through it, this is an indicator of the colour & clarity discharging from the filter, it will become cloudy after a few seconds. When it has turned from cloudy to almost clear the filter is sufficiently clean. Usually this only takes about 1 minute.
6. Turn off the filter pump
7. Push down on the multiport valve handle and turn it to “RINSE” rinsing flushes any cloudy water remaining in the filter down the waste line. Miss this step and you are likely to have a cloud of dirty water returning to your clean pool. Rinsing the filter for about 15-30 seconds is usually enough to ensure the sight glass is completely clear.
8. Turn off the filter pump then push down on the multiport valve handle and return it to the “FILTER” position and make sure it has locked back down in place.
9. You can switch the pump back on to check everything is normal and check the pressure on the gauge. This should be lower than before you started, jot this down so you can monitor how much it increases to guide you in the future.
Return your system to AUTO mode if you have an automatic timer and remember to close the valve on the waste line if you have one.
Congratulations you’ve now completed a backwash, helping to maintain your pool quality and the lifespan of your pool equipment!
This is a generic guide only and should be accurate for most pools and filters however there are always unique circumstances so it is always best to contact your local pool store or mobile service provider if you are unsure about your equipment or how to perform a backwash.
