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Commercial Sand Filtration

Properly functioning sand filters play a key part in keeping the water in top shape for commercial pool patrons. Photos courtesy Pentair

Ensuring cleaner and clearer water for pools

By John Watt

Every aquatics facility manager values the importance of cleaner, clearer pool water. To help ensure the best water quality in a commercial pool, the equipment needs to be operating in peak condition. Properly functioning sand filters play a key part in keeping the water in top shape for patrons.

Many facilities use sand filters because they are highly effective when backwashed properly, and the flow rate is kept on target. Unfortunately, improper backwashing and flow can lead to poor water quality or caliche, a rock-like material that must be chiselled out to get the filter back into working order.

To prevent a sand filter from becoming clogged with caliche, professionals must know about a phenomenon called channelling, including how to identify it, how it occurs, and the steps required to prevent it.

What is channelling?

Understanding the basics of sand filter operation can help ensure against the problems that cause channelling.

When the system kicks into filtration mode, the diffuser at the top of the filter evenly sprays water over the surface of the sand bed. The water then settles down through the sand and goes back into the pool, presumably cleaner than when it entered.

For these filters to operate correctly, the water must flow evenly through the sand bed. This enables the sand to properly filter out any debris.

Channelling occurs when water travels through smaller paths in the filter sand, which prevents it from flowing evenly through the sand bed. When the sand becomes dense and compacted, it hardens, and the water is forced through a very small channel from the top of the filter down to the laterals, without actually passing through the sand.

Essentially, the water flows right down the centre of the channel to the bottom of the filter and right back into the pool. When this happens, the water is no longer being filtered, resulting in poor clarity.

Operators can identify when channelling begins by performing a regular visual inspection of the sand. When looking down into the filter, the entire surface of the sand bed should be flat. If valleys and gorges are present, channelling has started.

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