Can a sand filter or cartridge filter be too oversized?

The simple answer? “No” Okay, blog entry done, move along!

In all seriousness, here at Mr Pool Man, we always tell our customers to get the biggest filter that fits their budget simply because of all the advantages an oversized filter brings to the table.

But before we dive through, here's our pool guru Tom with a quick overview on how to choose the right filter for your pool! 

Here’s a quick challenge. Take at your current filter (or over the internet if it’s too hot outside) and look for your filter’s minimum flow rate. If you’re saying that this is a trick question, then you’re absolutely correct. Aside from the recommended flow rates and maximum flow rates, there’s no such thing as a minimum flow rate for both cartridge filters and sand filters. If you have a huge filter, it may take a longer time to fill it up the first time, but once everything is up and running, it will filter your pool water just fine.

We have an in-depth discussion on the difference between a sand filters and cartridge filters in a separate article. Learn more by clicking here.

It’s pretty basic, a larger sand filter or cartridge filter means that there’s more filter media to trap dirt and debris. More filter media equals more time in between cleanings. Now why is this important? Well, if you’re the type of person that enjoys backwashing every few weeks under the blazing Australian sun or cleaning your filter cartridge every month while the heat and humidity dries you out, well then more power to you!

With a large enough filter size, you can get away with checking your filter’s pressure gauge even once a month or more, as compared to getting a filter that’s sized “just right”. And as an added bonus, you also save water by lessening the need for backwash cycles or hosing down your filter cartridges.

More time in-between filter cleanings mean more time in the pool relaxing!

As with real life, the less stress we have on our filter media means a longer lifespan! This is the main reason for the maximum flow ratings for filters. Higher flow means higher stress on the elements, higher/faster dirt and debris accumulation, and constant cleaning cycles. All of this adds to shortening of the lifespan of your filter media elements.

Your pool pump has one job and that’s to draw water from the pool and push it through the filter, that’s it. Before you say “A bigger filter will give the pump a harder time because it has more filter elements to push water through!” That’s a really valid question, but remember, filter elements are designed to let water through!

Your filter elements don’t trap water, they let them through easily. The only thing they trap is the dirt and debris that are in your pool water.

To make it easier to understand, let’s look at a sample, we used round numbers as to easily demonstrate the numbers to make the math as simple as possible. Let’s say your pool pump outputs 200LPM (liters per minute) and your filter is rated for a recommended/maximum of 150LPM. What this means is that your pool pump is pushing 50LPM more than what your filter is rated for.

This presents two problems. The first is that your pump is pushing more water through your filter that it’s designed to handle. This stresses your filter and filter elements, lowering its total lifespan! The next problem falls on your pool pump, since it’s pushing out 200LPM through something that is only allowing 150LPM to pass through unhindered, it’s meeting a resistance of 50LPM, this means that the pump has to work harder to push water through the resistance, adding more stress to the pump’s motor.

Now this can either lead to your filter breaking, your pump motor giving up, or heavens forbid, both breaking. If you’re lucky, you can get away with some repairs, but if they break, then you will be looking at hundreds, if not thousands of dollars in repair costs.

Now let’s look at the reverse. If your pump has an output of 150LPM and your filter is rated to accept 200LPM then that means that water is flowing through your filter with very little resistance so very little or no stress is placed on your filter elements. On top of that, you have an extra allowance for when the filter flow rate is being reduced by the dirt and debris that are trapped within your filter elements.

Do you remember your filter’s pressure gauge? The increase in pressure readings is an indicator of the pressure inside your tank. The pressure level will only go up if the water is having too much trouble going through the filter media. The two situations where water will have trouble going through the media is if the pump is too strong, it’s pushing more water than what the filter is allowing, so we’ll see a pressure build up.

On cartridge filters, this will show as a spike in pressure. On sand filters, this may cause channeling, or simply put, the water will create a “channel” or a gap in the sand that so that water can flow easily through the media.

SEE ALSO: What is the Best Pool Cartridge Filter?

So what’s the best combination? Can we just get a small pump and a large filter and be done with it? Well, the answer is a definite yes. But for maximum efficiency and flexibility, we suggest that you go with a large filter and a variable speed pump so that not only would you be maximizing the filter’s efficiency, but you’ll have the option of running the pump at faster levels during heavy days.