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How To Backwash a Pool Sand Filter

How to Backwash a Pool Sand Filter

Turn off the pool pump. Set the filter valve handle to the ‘Backwash’ position and ensure the handle locks in place. Turn the pump on and backwash for 2 minutes or until the water in the sight glass (located on the filter) is running clear. Turn off the pump. Set the filter valve handle to the ‘Rinse’ position and ensure the handle locks in place. Turn on the pump and run the rinse process for 1 minute or until the water in the sight glass is clear. Turn off the pump. Reset the filter valve to ‘Filter’ and ensure the handle locks into place. Turn on the pump.

All sand filters use the same basic mechanics: when set to ‘Filter’, water flows from the pool, through the filter, and back into the pool. The sand inside the filter system blocks debris, dirt, and oil. A typical sand filter multiport system has 6 different settings – ‘Filter’, ‘Backwash’, ‘Rinse’, ‘Circulate’, ‘Closed’, and ‘Waste’.

However, when you vacuum your pool, a concentrated level of dirt and debris get deposited into the sand – the result being that the sand becomes dirty and clogged with contaminants that, if left unchecked, will reduce the sand’s ability to filter and, ultimately, end up back in your pool, reduce the clarity of the pool water. Backwashing prevents this. Backwashing reverses the flow of water, lifts up and flushes the sand, and then expels the dirty water via a waste line into the ground or drain.

In order to prevent residual blow back into the pool, once you’ve finished backwashing it’s highly advisable to rinse the filter. Just as the backwash lifts and flushes the sand, the rinse resets the sand to its original position for optimum filtration.

How Often Should You Backwash a Pool Sand Filter?

As a general rule of thumb, you should backwash and rinse your filter about once a fortnight. The optimal time is right after you vacuum the pool. However, if your pool has had a lot more use than normal, it may be necessary to backwash once a week.

You can also tell when it is time for a backwash by checking the sand filter system’s pressure gauge. Normal operating pressures are between 50 and 75Kpa. When the sand gets dirty and clogged up, however, the pressure reading rises. If the Kpa pressure on the gauge is north of 80Kpa, it’s time to backwash.

Also, if leaves are prone to falling in your pool, more frequent back washing may be necessary since leaves, and other debris and contaminants will be entering your pool.

When Shouldn’t You Backwash?

If your pool contains an unusually high level of dirt, for instance, as a result of a nearby construction site, an extended period of being untended and uncovered, or possibly from runoff caused by flooding, it may be advisable to by-pass the filter entirely. In some cases, it may be better to vacuum directly to ‘Waste’, and send the vacuumed water directly down the drain.

A Few Important Backwashing Tips

The one downside of sand filter back washing is that, because water is expelled from the system and sent into waste, is that it…well…wastes water. While this is unavoidable, the key to not overdoing the backwash process and flushing out more water than strictly necessary is to keep a careful eye on the colour and quality of the water in the sight glass.

Don’t backwash more than necessary, or for longer than necessary. Sand filter systems operate most efficiently in the middle of the filtration cycle. This is partly due to the positioning, at any given time, of the sand in the filter, and, partly, because of the cyclical build-up of collected dirt and debris in the filter. The net effect is that too much, or too frequent, backwashing actually reduces the sand filter’s efficiency.

Finally, make sure you always turn off the pump before you either move or reset the filter valve setting. If you don’t, you’re going to damage, and maybe destroy, the system.

Reduce the Need to Backwash

As we mentioned earlier, leaves and other debris can lead to you needing to backwash your pool sand filter more often or even dump the water out if the water gets too dirty. One of the best ways to prevent this from happening is to invest in a good pool cover.

Make Backwashing Easier

Sometimes backwashing becomes difficult when the sand media becomes gunked up and the efficiency of your sand filter is reduced. If you have a fairly new sand filter or if it hasn't been at least three years since you have installed/changed your sand filter media then it might be a good idea to give your sand a good soaking with some Water TechniX filter cleaning solution.

It's a very simple to do. Simply take off the multiport valve, pour in a bottle of filter cleaning solution, allow it to do its magic for 24 hours (Remember, directly in the sand filter and not in your pool!), return the valve, backwash thoroughly and that should be it! Your sand filter's elements should be good as new, or as close to it as possible! If that doesn't work then it may be time to change out your sand for new one.