How to Choose the Right-Sized Filter for Your Pool

You might have heard that the pool pump is like the heart of your circulation system, since it’s what powers circulation in the first place. If so, the filter is its liver. That means it kicks out toxins before they can do any harm. Kapow.

And boy oh boy, does your pool have to deal with some serious stuff. Contaminants include debris like twigs and leaves, bacteria that contain viruses, and even organic matter like the natural oils of your skin. 

All of this has the potential to exhaust your sanitizer and put a swift end to safe swimming—and absolutely would, if you didn’t have a pool filter suited to your larger system. I’ll explain how the pump works with the filter, which filter type is right for you, and how to get the right-sized filter for your pool.

The Power Couple: Your Pool Pump and Pool Filter

This is one dream team. That fun and relaxing body of water you’ve got in the backyard is actually home to a lot of gunk, too. That’s because of bacteria that invites itself to every pool party. Especially in warm water, the bad guys can thrive and reproduce.  

And the more particles that are already in your pool, including debris like leaves and organic matter like swimmers’ hair oils and more, the harder it is for your sanitizer to wipe them out.

Without your pool pump, you wouldn’t have a pool at all—more of a nasty swamp before you know it. Your pump circulates water throughout your larger system. This gives your chemicals a chance to evenly distribute across your water, the skimmer and the pump’s strainer basket to remove large debris, and your pool heater to keep your water at a comfortable temperature. 

It also allows your pump filter to do its job. And that’s a big deal. 

So what exactly does the pool filter do? It’s yet another indispensable defense against the contaminants in your pool water. Though your pool sanitizer might neutralize bacteria in your pool, the filter is what actually removes them.  

Without a pool filter, your sanitizer would be exhausted, your water would be cloudy and nasty, and it could be potentially dangerous to swim—because some of the bacteria found in pools can make you sick. 

So, yeah. You’re not going to want to skip on this one. But even more to the point: for clean, safe waters, you want to make sure you have the right filter. Capiche?  

You Got the Right Filter Type, Right? 

Ready to choose the best filter? Well, you’ve got three pretty solid options: the sand filter, the cartridge filter, and the Diatomaceous Earth (D.E.) filter. All differ in cost, maintenance, and how often to replace the media inside. 

They also differ in efficiency. The smallest unit of measurement for these nasty particles is called a micron. Be sure to keep an eye out (figuratively, since a micron is invisible to the naked eye) for up to how many microns these types can filter out. The smallest of bacteria can be as microscopic as two microns. 

Psst... not feeling like hitting the books right now? My recommended filter is the sand filter with glass media. But feel free to pretend I never said that and read on.

One key to lengthening the life of your pool filter: switch from a manual vacuum to an automatic cleaner. The Blue Torrent Stinger Automatic Pool Cleaner is my top recommendation. It works independently of your filter which lowers energy costs, just needs to be plugged into an outlet, and has an included warranty. 

The Classic: Sand Filter 

There is a ton of outdated equipment in the pool industry that companies will try to sell to you as “the standard.” I’m thinking especially of single-speed pumps, which actually cost a fortune in operation over the years—and end up being much more expensive than the high-tech, market-topping variable speed pump.  

The sand filter, on the other hand, is a pool classic that isn’t broken—so no need to fix it. It’s the standard, and it still works great.  


- Sand filters are most affordable filter type on the market.

- The jagged edges of sand can filter up to 20 microns.

- Replace the sand with Zeosand or glass filter (my favorite) to filter up to 5 microns.

- If using glass filter, use only 1/5 of the amount you would sand, and no need to replace the media for 10 to 15 years.

- Glass filter also has a negative electric charge, which attracts nasty bacteria. 


- If you use sand media, 20 microns is actually pretty inefficient compared to the 5 microns of Zeosand and glass filter.

- Sand media and Zeosand need to be replaced every 5 years.

- To clean your sand filter, you need to backwash it—keep an eye on the pressure gauge to know when. Backwashing can be a hassle and waste water. 

Efficient and Easy: Cartridge Filter 

Cartridge filters are like the smart cars of pool filters: they tend to be on the smaller side, they’re easy on the environment, and they aren’t exactly made of horsepower. They’re a great pick, as long as you don’t have an extremely powerful pump or a giant pool.

They’re also more efficient than the traditional sand filter with sand media. A cartridge filter can kick out bacteria as small as 10 microns.


- No need to backwash. Ever. This saves your pool’s energy and a lot of your time.

- The cartridge media runs cheap.

- Without backwashing, you’re not wasting water.

- Since cartridge filters work great at low speed, this is the perfect companion to your variable-speed pump. You do have a variable-speed pump, right?


- You’ll need to rinse your filter down every 2-6 weeks. 

- The inner cartridge will need to be replaced every 2-3 years. That’s the most frequent replacement for any filter media.

- Massive pool? Nice. But this probably isn’t the filter type for you.

A cartridge filter sounding pretty good right now? The Black Diamond 30 Cartridge Filter with Blue Torrent Pump is my top recommendation. It guarantees less frequent servicing, includes an auto-check valve, and contains the finest, most durable cartridge material on the market. 

Danger is My Middle Name: D.E. Filter

This is the type I recommend the least—for a few important reasons. First of all, operating a D.E. filter is straight up unsafe.  

D.E. filter tanks contain what are called “fingers,” or grids of crushed fossil remains of a hard-shelled algae group called diatoms. These have the same properties of sand media. But unlike sand media, they’ve been proven to be carcinogenic.


- D.E. filters can filter down to 5 microns—but remember, a sand filter with glass media can do the same. 


- D.E. is a known carcinogen, and can give you a lung disease called silicosis. If you do use it, wear a mask when handling.

- It’s the most expensive filter type.

- It’s the highest maintenance filter type.

- Backwashing D.E. is harmful to the environment, and in some places, it’s even illegal. 

How Filters are Sized 

Like any equipment that you add to your greater circulation system, your pool filter should fit both the pool’s size (that’s the number of gallons of water it holds) and the other equipment you’ve got hooked up. 

Since your pump is the power-driver behind your system, it’s especially important to make sure your pump is sized for your pool, your filter is sized for your pool, and your filter is sized for your pump. 

Interested in saving money? Checking off these boxes will help get your pool one step closer to energy-efficient.  

How to Choose the Right Filter for You—Pool Size 

It’s essential to make sure your filter works for your pool size. If you buy a filter too small, it just won’t do the job, and you’ll be swimming with bacteria. Buy a filter too big and you’ll waste money on your energy bill every month.  

Another note: when sizing your filter to your pool size, be careful when reading the manufacturer’s instructions: they have a tendency to overshoot just how much their filter can take on.  

See the chart below to get it just right—and if you’re not sure how to calculate the size of your pool, now is the time to do it. 

How to Choose the Right Filter for You—Pump Size

Your pool pump needs to be just strong enough for water to be sucked in from your pool and pushed out through your filter. And no, that doesn’t mean you should go out and get the most powerful pump on the market—too much horsepower and you’ll be losing a lot of money every month on energy costs. 

Keep in mind that pool filters are sized from gallons per minute per square foot, not the actual size of the unit. Don’t worry—that largest cartridge filter won’t take up your entire backyard and then some. 

See the chart below to match your horsepower with your pool filter.   

Got a big pool? Lucky you! Keep it in top shape with the ultra-powerful Black & Decker 3 HP Variable-Speed Pump. It includes a warranty, qualifies for utility rebates, and pays itself off in up to 80% energy costs saved in all stages of operation.

No Filter? I Don’t Think So! 

A little work now and you’re set for years to come. It’s a shame pool owners often overlook the importance of a perfectly-sized filter. Now that you’ve figured out what size is best for you, you’ll be saving money every single month on operation costs. Plus, your pool is cleaner and safer than ever. That calls for a little celebratory cannonball, don’t you think? Enjoy.


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