We all need to lean on someone sometime. But when it comes to your pool filtration system, each part is completely dependent on the rest; when one piece goes awry, the entire cleaning process gets backed up. So although I’ve covered how to sanitize your water with chlorine and pool shock, it’s high time we make sure your pool filter is up to speed. Here I’ll explain what it is, how it works, and how to choose the right one (and size) for you—because nobody wants to swim in what could pass as old bathwater. No, thank you.
What’s a Pool Filter?
A pool filter is a standalone unit connected through plumbing to your pool circulation system. While the sanitizing chemicals you add to your pool might kill contaminants, your pool filter is what actually removes them. After your water is pushed through the pump, it goes through the filter before returning back to your pool—cleaner and safer than ever. Ta da.
Doesn’t My Pump Already Have a Filter?
This is a major misconception. Your pump may have a built-in feature that is commonly called a filter or strainer. And many people think that that’s their filter, and wonder at the increasingly murkiness of their pool.
What a pump strainer actually does is separate out all the larger pieces of debris, such as leaves and twigs. An actual pool filter stops smaller particles, such as bacteria, from re-entering your pool water.
Does a Pool Filter Really Do That Much?
Boy, does it ever. Meet the micron, the unit of measurement that filters remove. It’s short for micrometer, which is one millionth of a meter. For reference, a piece of human hair is 50 microns, a white blood cell is 25 microns, a unit of household dust is 4 microns, and bacteria, some of which is pathogenic and can make you sick, is 2 microns. I’ll let that sink in.
How Do Pool Filters Remove Microns?
Essentially: it’s a trap. Each filter has what we call filter media, which is the actual material that traps particles and keeps them from returning back to your pool. The finer the material, the more microns of dust, dirt, and sand it can catch. The really efficient filters can also trap bacteria—and remember, if you get serious about sanitizing your pool, those viruses are already killed and rendered inactive.
If the filter is the liver of your circulation system, the pool pump is the heart. Get a variable-speed pump before it’s federally mandated next year, and never look back: the 1.5 HP Energy Star Blue Torrent Variable-Speed Pump will pay itself off in under one year, is eligible for rebates, and comes with a lifetime warranty.
Okay, I Definitely Need a Pool Filter. How Do I Choose?
Three types: sand filters, cartridge filters, and Diatomaceous Earth (D.E.) filters. Each has their own pros and cons, which I’ll list out here. Spoiler alert: personally, my favorite combination for a standard pool is the sand filter with the glass filter. Got a little more time? Pretend I never said that, and read on.
Sand Filters: A Little Rough Around the Edges.
Sand filters are perfect when you want a dependable filter on a lower budget. They’re also fairly effective, and typically catch particles as small as 20 microns—and even less if you replace the standard #20 silica sand with another media. Get ready for some pretty good options.
How Sand Filters Work.
After your pool pump pulls water from your pool, it pushes that same water through its own strainer, and then over to the sand filter, which is full of #20 silica sand. Because each grain of sand is sharp around the edges, these jagged borders catch contaminants that pass through.
How to Care for Your Sand Filter.
Remember, not everything lasts forever: over time, the water passing through will erode the silica sand and smooth it out. Without rough edges, the sand will have nothing to catch the contaminants. Plus, the volume of debris will fill up in the tank. Though this might help the filter work efficiently in the beginning, eventually the pressure will decrease the water flow.
The side of the filter will have a pressure gauge, which will alert you to increasing internal pressure. Once this pressure has built up, it’s time to backwash your filter. This involves using a backwash hose to reverse the water flow and flush the debris to waste. If you loose a little sand in the process, no worries—that’s normal.
Backwashing aside, you’ll need to replace your smoothed-out silica sand once every five years or so. Don’t worry, this is something you can definitely do yourself—just make sure your system is powered off first.
Replace the Sand, Get Better Results.
Although 20 microns might sound impressive, remember that bacteria is often just two microns. You’ll need to either really be on top of your sanitizing chemical game—which you should be, anyway—or replace the #20 silica sand with a better alternative: either ZeoSand or glass filter.
Zeosand is made from the mineral zeolite, and has even rougher and smaller edges than #20 silica sand. Thanks to this advantage, it can filter down to 5 microns. Like silica sand, it’ll need to be replaced just about every five years or so—but you’ll actually only need half as much than sand to fill up your tank.
Glass filter is my favorite: finely cut glass made from 100% recycled materials, filters as small as 5 microns, and lasts up to 10-15 years in your tank. Plus, it has a negative electrical charge, so positively-charged contaminants are even more drawn to it. You can also use about a fifth less in your tank than you would silica sand—but with a longevity at least double than that of silica sand, you’re already saving a significant amont of time and trouble.
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The Sand Filter Pro List.
- It’s inexpensive, and commonly used.
- You have a range of media options to load into it.
- Maintenance is fairly easy and straightforward.
The Sand Filter Con List.
- Although backwashing is easy, it can feel like a hassle—and waste water.
- 20 microns might seem like it’s a lot, but it’s worrisomely low.
Cartridge Filters: Energy Efficient Means Money Saved.
Cartridge filters are great—as long as you don’t have a big pool. Think of these as the smart cars of pool filters: they tend to be smaller themselves, are easier on the environment, and aren’t exactly made of horsepower. They’re also a little more expensive than sand filters. However, they don’t require backwashing, their cartridges run cheap, and they filter out as small as 10 microns.
How Cartridge Filters Work.
Instead of freewheeling sand, cartridge filters contain a capped plastic cylinder which holds pleated polyester filter media. When water flows through this polyester, the fibers catch the contaminants, and the water returns to the pool largely clean and debris-free. It’s that easy.
How to Care for Your Cartridge Filter.
Forget backwashing. For the cartridge filter, all you need to do is turn off your system, remove the cartridge from the tank, and spray it down with a hose. If the hose isn’t showing a dramatic change, try spraying it down with a filter cleaner. You’ll also want to soak it in a chemical filter cleaning solution like diluted muriatic acid every 6 weeks or so.
Of course, all that cleaning won’t prevent the inevitable: you’ll need to replace the cartridge every 2-3 years.
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The Cartridge Filter Pro List.
- I’ll say it again: no need to backwash cartridge filters.
- No wasted water, so it’s better for the environment.
- These work great at low speeds. If you have a variable-speed pump—as you should—this is the filter for you.
The Cartridge Filter Con List.
- Rinsing your filter down every 2-6 weeks can be a bummer.
- Each cartridge only lasts 2-3 years—which is a more frequent replacement than any other pool filter.
Diatomaceous Earth (D.E.) Filters:
The D.E. filter has been long understood as the most ambitious of pool filters, since it’s more expensive and higher maintenance. But in my opinion, it’s not worth the hassle for filtering down to 5 microns—you can get the same results from glass filter media in a standard sand filter. Plus, this filter media can actually be a health hazard. Check out my con list below.
How D.E. Filters Work.
D.E. filter tanks contain what are called “fingers,” or grids of crushed fossil remains of a hard-shelled algae group called diatoms. Like the standard media in sand filters, diatoms are also made of silica, and have the same containment-catching properties.
How to Care for Your D.E. Filter.
Similar to sand filters, you’ll know when to backwash based on your pressure gauge, and the system should be the same. However, it’s important to note that used D.E. builds up to a concrete-like substance that can clog storm drains and be ecologially harmful. For this reason, many cities and states have specific laws for where your D.E. should go when its time is done. In most cases, you can seal the used powder up and put it in the trash, but you’ll want to make sure to check your local measures—the D.E. filter is expensive enough without additional fines.
Many D.E. models also have a bump option, which allows the used up D.E. powder to fall off the grid for cleaning.
Whether you backwash or bump your D.E. filter, you’ll need to replace the powder, which is much more effective to do through the pool’s skimmer. To do this, you want to mix the manufacturer’s recommended amount of D.E. with water to form a wet sludge, and then pour the solution directly into the skimmer. It’ll take some time for the mixture to properly disperse across the filter, so you’ll want to wait at least eight hours until you swim again.
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The D.E. Pro List.
- D.E. filters as small as 5 microns—but again, a sand filter with the right media can do that.
The D.E. Con List.
- D.E. is a known carcinogen, and can give you a lung disease called silicosis. If you use it, wear a mask whenever handling.
- It’s the most expensive filter on the market.
- It’s the highest maintenance filter on the market.
- Backwashing D.E. could be illegal, depending on where you live—and harmful to the environment no matter what.
How to Choose the Right-Sized Pool Filter.
This is where the search gets serious. Before going on to this step, make sure that you currently have the right-sized pool pump—the filter you choose will depend on your pump, and if your pump isn’t right, the whole system lacks efficiency.
Sizing Your Filter to Your Pump.
Remember, your pump is behind it all. In order for the water to be sucked in from your pool and pushed out through your filter, your pump needs to be just strong enough. 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. See the chart below to match your horsepower with your pool filter.
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.
[INSERT CHART NUMBER 1]
Sizing Your Filter to Your Pool Size.
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. And just like what will happen if you buy the most powerful pool pump on the market, a filter that’s too big for you will waste money on your energy bill every month.
See the chart below to get it just right—and if you’re not sure how to calculate the size of your pool, might as well check out my how-to here, and learn how long to run your pump while you’re at it.
[INSERT CHART NUMBER 2]
You’ve got the pool filter you need—but that doesn’t mean you’re done. Be sure to scrub your pool periodically for any particles that might stick to the walls and floors. My recommendation is the 360-Degree Bristles Blue Torrent Pool Brush, which is patented and was developed by longtime pool servicers.
Now Get Swimming—With Only the Guests You Invited.
So long, bacteria, viruses, and tiny pieces of debris. This pool is only for humans now, and the occasional skillful dog. Now that you have the perfect pool pump, you don’t have to float along with the inactive particles your chlorine has attacked. It’s just you, and the people you want around—and your energy bill will thank you. Have a happy and safe swim. Enjoy.