When it comes to swimming pool maintenance, few things are as important as the filter: Your filter system keeps your pool water sparkling clean and free of debris and harmful bacteria. It helps ensure that your chemicals work effectively and your water is balanced.

This is a big job, and your pool filter can’t do it alone. If you want to keep your filter operating at peak performance, you’ll need to learn how to take care of it properly. We’ll start with one of the most important – but most often overlooked – parts of pool filter maintenance: Learning to read and understand the pressure gauge.

A pool filter pressure gauge is the gadget that reads the amount of pressure building up inside your filter. A typical pressure gauge is round, with an indicator needle and a maximum reading of 60 PSI.

Know the Lingo: Pounds per Square Inch

Pounds per square inch – sometimes called “PSI” for short -- is a unit of measurement that is used to read air, gas, or liquid pressure. Even if you’re new to swimming pools, you might be familiar with PSI from measuring the air pressure in your car’s tires.

Understanding Your Pressure Gauge: Know What’s Normal

Pressure gauges aren’t terribly complicated devices, but they play a critical role in your filter’s performance. Pressure keeps the water moving through your filter system -- so when your water pressure is too high or too low, your water quality will suffer.

The first step in understanding your pressure gauge is knowing what is considered a normal PSI range for your filter. For pool owners, the normal range is around 10 PSI; check your owner’s manual for more information.

Once you know what’s normal for your filter, get in the habit of checking the pressure gauge once a week as part of your pool maintenance routine. As long as the water pressure is in the “normal” range, you can rest assured that your pool filter is in good working condition.

What should the pool filter pressure gauge read?

When it comes to swimming pool filter systems, all systems operate a little differently. Check with your manufacturer or ask your pool professional to find out what’s considered “normal” for your model.

Pressure Too High? It’s Time to Clean the Filter.

Generally, if your pool filter water pressure rises more than 10 PSI over the normal range, it’s time to clean – or possibly even replace -- your filter. For most filters, 20 or 30 PSI is considered too high, but you should consult your pool professional to make sure that’s true for your model.

If you’ve cleaned the filter recently and you’re still showing an above-normal PSI, check for leaks in your filter system.

Meet Your Pressure Gauge’s BFF: The Air Relief Valve

The air relief valve works hand-in-hand with your pressure gauge to keep your filter running smoothly. The air relief valve provides a much-needed outlet for releasing air that gets into your filter system, causing pressure to rise. In general, you want to release air through this valve after any maintenance activities that could introduce air to your system, such as cleaning or backwashing your filter.

Pressure Too Low? Look for Blockage

If your pressure gauge indicates that the PSI is lower than normal, you may be dealing with blockage: Check your skimmer baskets and all the lines in your filter, and clear out any large debris or clogs. A few other common causes of low pressure problems? Your pool’s water level might be too low or your pump might be too small. And don’t forget to check for leaks. Depending on where they’re located, holes or leaks can cause low pressure, too.

The Three Types of Swimming Pool Filters

Every swimming pool system – salt water or fresh; inground or above-ground; vinyl, gunite, or fiberglass – needs a filter. There are hundreds of models to choose from, but all of them fit into one of these three categories:

Sand Filters – Inexpensive and easy to operate, sand filters remove dirt and debris through a process called “backwashing,” which basically means flipping a switch to reverse the water flow

Cartridge Filters – Cartridge filters remove more dirt and debris than sand filters, and they don’t require backwashing. Instead, you simply remove the cartridge when it becomes too dirty and hose it off.

Diatomaceous Earth (DE) Filters – Like a sand filter, a DE filter requires backwashing. However, unlike sand filters, DE filters only need to be backwashed a few times a year. DE filters are expensive, but their filtration capabilities, superior to both sand and cartridge filters.

Replacing Your Pressure Gauge

If you’re getting incorrect or inconsistent readings – for example, your PSI is sky-high one day and well below normal the next, or your gauge is reading high or low for no reason – it may be time for a replacement. You should also replace your pool filter pressure gauge if it’s cracked, rusted, or showing any other signs of wear.

The good news is pressure gauges are inexpensive and relatively easy to replace. You can buy a replacement at any big-box or pool supply store.

Pro tip: Remember to turn the pump off and use the air relief valve before you replace your pressure gauge!