An open backwash is an important step in the regular maintenance of your pool, but so many pool owners don’t know how to do it.

open backwash pool
Welcome to our top tip on maintaining a sparkling pool! Keeping a pool clean is actually quite simple, as long as you know what to do – and this is one thing you should be doing. Before we tell you how to perform an open backwash, let’s have a look at how your pool filter works:

Your pool’s filtration system is the heart of it – it’s what keeps the water clean and inviting through summer. The system works by pumping water through a filter filled with silica sand, which traps contaminants like hair, dust and suntan lotion. Silica sand is characterised by its jagged edges and cracks, which you can see if you look at a grain under a microscope. It is these cracks that allow it to filter out impurities down to 20 microns in size – about half the width of a human hair.

open backwash pool
As good as silica sand is, it tends to clump together over time. Water will form little channels through the clumps and flow along these channels instead of through the sand itself. The result? Water that isn’t being properly filtered, which means a murky pool and increased chemical usage.

A common misconception is that simply backwashing the pool (reversing the flow through the filter to clean it) solves the problem. However, this method only cleans the channels formed by the water, not the entire filter and all the sand in it.

This is why you need to do an open backwash at regular intervals. An open backwash is a deep-cleaning process that resets your filter and gets it working well again. Unlike a standard backwash, an open backwash requires manually mixing the sand within the filter, ensuring water flows through the entire filter compartment for a comprehensive clean. This method may seem intimidating and a lot of work, but it’s surprisingly straightforward and can significantly extend the life of your filter sand.

open backwash pool
With the pump off, start by removing the filter housing lid with a hand screwdriver. Make sure that you prevent dirt or sand from entering the screw holes during this process or you could end up with a problem like jammed nuts or a leaking filter. To do this, simply pop the screws back into the holes and hand tighten them after you’ve removed the filter lid. Also, cover the breather pipe with a packet to keep it clear.

Set the multiport selector to backwash and turn the pump on.

open backwash pool
During the open backwash, it’s normal for water to overflow from the filter housing. Put your arm into the filter and use your hand to stir the sand, breaking up any dirt clumps. There’s nothing dangerous in there so you don’t have to worry about your fingers being injured, but do take off jewellery and watches, because the sand is very abrasive. Be careful to avoid damaging the interior of the filter.

Once the water coming out of the filter starts to run clear, the sand is clean. Turn off the pump, wipe the filter’s top and then carefully reattach the lid. Tighten the screws with a hand screwdriver in a diagonal sequence for uniform pressure. Don’t be tempted to speed things up by using power tools or you may end up damaging something.

open backwash pool

The final step is to activate the rinse mode on the pump to wash out any leftover dirt. Once the water is clear, switch the system back to its filtering mode.

If you perform an open backwash and you still find your pool cleaner slowing down or your pool becoming murky, it might be time to replace your filter medium. Traditional silica sand can be substituted with Eco Fibre, an environmentally friendly alternative made from recycled plastic bottles. Eco Fibre offers the added benefit of being water-wise, requiring only occasional rinsing rather than frequent backwashing.

open backwash pool
We know that nobody welcomes an extra maintenance step, but an open backwash doesn’t take long to do and doesn’t have to be done very often, so it is something you should definitely add to your pool-cleaning regime.

Builders stocks Eco Fibre, silica sand and everything else you need to keep your pool sparkling all year round, both in-store and online at

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