Just How Important is a Filter?

All too often chemicals are blamed for poor water quality when in fact the root cause is more often than not, insufficient filtration. If a domestic pool owner only runs their pool pump for a few hours a day, they are relying far too much on the disinfectant (e.g. chlorine) in the water to keep the pool safe, clean and crystal clear. Moving water is safe water! This also applies to public swimming pools. The more filtration and circulation of the water the better the quality will be and the easier it will be to maintain. It is important to ensure that the water passes through the filter media at the right speed. Too fast and any captured debris is pushed through the media and back to the pool. The slower the water passes through, the better and more efficient the media will be. In fact, if you simply half the speed at which the water passes, you will increase the filter efficiency by 4 times. Beware, if you reduce the speed of the pump, you will ultimately slow down the circulation of the water in the pool tank. This can result in dead spots with bacteria and algae taking hold. Unless a filter with a larger surface area can be installed, you may need to compromise with variable speeds to achieve a slower filtration speed for part of the day and increase the speed for the rest of the day to maintain good circulation.

What goes in, must come out. The purpose of the filter is to capture any physical debris from the water. This debris builds up over time to the extent that it will reduce the performance of the media and begin to block up. This is why the backwash process is just as important as is achieving an efficient filtration speed. What ever the media used, it’s important to get fluidisation of the media bed in order to release all the captured debris. According to German DIN standard, where sand is used as a filter media, the required speed for backwash is 60m/h (m3/m2/h). This requires a lot of water and also will not guarantee a break up of the ‘mud balling’ than occurs in sand. The result of an insufficient backwash is the reduction of filtration efficiency. Captured debris remain in the filter, harbouring bacteria and increasing the demand on the disinfectant used. It’s at this point that the water quality starts to suffer.

A more efficient backwash can be achieve at a slower backwash speed when glass media is used instead of sand. This stands to reason as glass is lighter than sand in weight so, less forces are required to achieve the same lift. We would recommend a speed of 45m/h to get the required fluidity. However, not all glass media will give the same filtration and/or backwash performance. The shape, size and colour of glass media available on the market vary considerably. Some are very round, almost sphere like. I liken this spherical media to the plastic balls you find in kids play pits. You can quite easily push your hand right through them. This demonstrates a lack of mechanical performance although I understand that it works well at very slow speeds in grey water applications. Other glass media are quite flat, a bit like piling coins on top of one another and will block up a filter very quickly resulting in the need for more frequent backwashing. Most will still be prone to ‘mud balling’ and encourage bacteria growth but, not to the same extent as sand.

AFM (Activated Filter Media) has been engineered to a specific shape and size and is available in various grades. It has been independently tested by IFTS (Institut de la Filtration et des Techniques Séparatives) out performing other medias. Because it is made from specially selected green and brown glass, the raw material already has a certain ionic charge to it. No other coloured glass carries an ionic charge at these levels. The charge is enhanced with further heat treatment and chemical processes. As a result, the surface of AFM is bio-resistant. No ‘mud balling’ can occur and bacteria cannot reach its surface. Captured debris is released very quickly during even the shortest of backwashes, resulting in huge reductions in water consumption and savings on heating for replacement backwash water. Disinfection demand is greatly reduced thus resulting in less disinfection by-products which, in turn results in a safer, more pleasant environment for bathers.

So, just like in the ’Pyramid of Pool Water Treatment’, if you get the foundation correct in the first instance with the correct dimensioning of the filter vessel, the correct flow rate, correct backwash speeds, the best filter media and you simply eliminate future water quality problems significantly.