Why Your Pool Pump Isn’t the Problem — Your Filter Is

Clear water starts with the right filter, not a monster pump. We dive into the real drivers of pool clarity and ease of maintenance, showing why filter sizing determines circulation, energy use, and how often you clean. If you’ve battled cloudy water, sluggish skimmers, or a cleaner that crawls, the culprit may be a filter that’s too small for your pool and conditions.

We break down how different filters behave under load. Large cartridge filters spread debris across big surface area, keeping PSI stable and flow strong for months. DE and sand deliver great clarity but show faster performance drop-offs as dirt builds, making the pressure gauge your best early warning. You’ll learn clean PSI baselines, the 10 PSI rule for action, and when a quick backwash can restore flow. We also map practical sizing: for around 15,000 gallons, a 300 to 400 square foot cartridge, a 60 square foot DE, or a 300 to 400 pound sand filter is a smart starting point. 

Pump horsepower isn’t the hero for every filter. Sand filters often perform worse with oversized pumps, while large cartridges can take advantage of higher flow without choking. We share field stories, from a 15,000-gallon pool that ran beautifully for years on modest pumps thanks to a 420 square foot cartridge, to the chronic struggles of above‑ground kits saddled with tiny 25 to 50 square foot filters. The message is simple: size the filter generously for your gallonage and lifestyle, track your clean PSI, and prioritize circulation as much as filtration. Your reward is clearer water, less maintenance, and a system that’s far more forgiving during storms, parties, and heavy pollen weeks.

• why circulation matters as much as filtration
• how undersized filters choke flow and raise PSI
• cartridge vs sand vs DE behavior under load
• reading clean PSI and spotting 10 PSI rise
• when to backwash and when to clean
• recommended sizes for 15k and larger pools
• why sand dislikes oversized pumps
• tandem cartridges and large-pool strategies
• above‑ground kit pitfalls and upgrades

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Chapters

• 1:50 Why Filter Size Matters Most
• 3:33 Undersized Pumps, Oversized Filter Lesson
• 4:33 Manufacturer Specs vs Real-World Needs
• 5:42 Filtration And Circulation Explained
• 7:05 Cleaning Frequency And Filter Area
• 8:09 Small Filters And Failing Flow Signs
• 9:34 Reading PSI And What It Means
• 12:13 Backwashing To Restore Flow
• 13:46 Matching Filter To Pool Size
• 15:17 Sand Filters And Pump Horsepower
• 16:36 Recommended Sizes By Pool Volume
• 18:06 Large Pools And Tandem Cartridges

Transcript

SPEAKER_00: 1:02

And welcome to the Pool Game Play Cash. In this episode, I'm going to talk to you about filter sizing, how to pick the right filter size, what happens if you have the wrong filter size, and why filter sizing is really the most critical thing for your swimming pool and for your pool care. Are you a pool service pro looking to take your business to the next level? Join the pool guy coaching program. Get expert advice, business tips, exclusive content, and get direct support. From me, I'm a 35-year veteran in the industry. Whether you're starting out or scaling up, I've got the tools to help you succeed. Learn more at swimming poollearning.com. And I would say the filter size is actually the most important aspect of your pool care. It's even more important than your pump size. I've had a pool that was brand new, fairly good sized pool. I think it was around 15,000 gallons. And no one knew this, but the builder kind of skimmed on the pool pump. And it wasn't until the motor burned out and we took it off that we discovered that he put three-fourth horsepower pumps into this pool. One had no, it was one pump for the spa and one for the pool. And I know the customer when he had the pool done is stated that he was going to get one and a half horsepower pumps. So for like 10 years, this thing is running off of three-fourth horsepower pumps, really with no problem, because it had a full-size cartridge filter. It was a 420 square foot Pinter Clean and Claire Plus. And so even though it I thought or I didn't know, but it was actually running on undersized pumps, the pool really had no problem because of the larger filter. So the filter, regardless if it's sand, DE, or a cartridge filter, getting the right size filter for the pool is really the critical thing when you're getting a pool built or when you're remodeling a pool or when you're taking over service for a pool. Now I know a lot of builders will go off of the manufacturer specs, and a lot of them will put in, and this is very common in Florida, but it's common here also when there's a fiberglass pool put in, that you're going to get a pool that, in my opinion, has an undersized filter. Now, of course, a 15,000 gallon pool with a 150 square foot cartridge filter is sufficient based on the manufacturer specs. But in reality, you're going to be cleaning that filter a lot. If the pool does turn, it takes longer to turn it back around. And I think that the best way to prevent problems with your pool care is to have a larger filter put in. And if you have a small filter, changing that out is also a factor and something that you may want to consider doing. And I think it's important to understand what the filter actually does for the pool and the filter and why the filter sizing is so important and an essential component to the pool. So the filter does not just filtration, but also helps with the circulation of the pool. This is an important aspect, especially if you're new to pool service and you haven't been around pools for a long time, or if you just bought a house at a pool, it's important to know that not only does the filter, pool filter, filter out, you know, algae, dirt, particles, things like that, it also helps circulate the pool. So the bigger the filter, the better circulation you're gonna have with the pool. And this doesn't really mean that you have to get a bigger pump. I mentioned the 3-4 horsepower pumps. It just means that you have to have a good size filter for the pool so that not only does it filter out all these things, but it also circulates the water properly in the pool. There's no dead spots, you're not running the pool, you know, 20 hours a day because of the poor filtration or circulation with an undersized filter. So when you look at the pool filter, you're not just looking at the filtration capacity, you're also looking at the circulation of the pool water itself as well. And it's a really important aspect of filter sizing because if you have a 100 square foot cartridge filter at a pool, let's say it's 15,000 gallons, and you have a 400 square foot cartridge filter at that same pool, and let's just say you have a one-horsepower pump, the amount of circulation you're gonna get out of the larger filter is going to add to the water clarity. It's also going to reduce the amount of time times you clean that filter during the season. For instance, if you had a 100 square foot cartridge filter, you're cleaning that thing every month, whereas with a 400 square foot cartridge filter, typically there's four cartridges inside there, you're cleaning that one maybe every four to six months. So that is also a factor with filter size, how often you have to clean it, and most importantly, the circulation of the water is a big factor. When the filter starts to get dirty, if it's a smaller filter, a hundred square foot cartridge filter versus 400 square feet, the fill the circulation is affected more dramatically. I had a group member that sent me a little short video of a skimmer, and the water wasn't moving at all, and the filter looked like it had normal PSI, it was at 20, but it was a 100 square foot cartridge filter, and I told him, you know what, just take out the element and replace it with a new cartridge, and you should that should solve the problem. And then, like the next day he sent me a video of that same pool, and he showed me the skimmer, and it was just pulling water in like crazy. Because again, the smaller the filter, the more impact as dirt and debris and algae get in there, the more impact that has on the poor circulation of the pool. With a 400 square foot cartridge filter, as it starts to get dirty, it has so much square footage and area that you really don't see the impact of it on the pool circulation. And a D filter is also one that is really sensitive to the impact of getting dirty. And for example, if you had a D filter, let's see, let's just say you had a 40 square foot D filter, which is really common in my area, and it starts to get dirty after you cleaned it like two months ago, and it starts to get a lot of dirt in there, and the filter pressure goes from 20 to 30 psi. Now on the gauge on top, there's a pressure gauge. I should probably touch on this for a minute here. The pressure gauge indicates how much pressure there is in the filter. The higher the psi, the more resistance you're gonna have in that filter, the dirtier it gets, the higher the psi will go. And that pressure gauge is really important because in most cases a clean cartridge filter will be around 10 or 12 or 14 psi, a clean D filter will be around 20 PSI, a clean sand filter will be around 20 psi as well, and then as the DE and sand filter start to get dirty or impacted by dirt and algae and things like that, the psi will rise because there's less water flowing out of the filter and more pressure in the filter. And so once the DE filter gets to 30 psi, you're gonna see a pretty large impact on the circulation of the pool. The first thing you may notice is like the spa spillway is just trickling now, it's not overflowing into the pool. You'll also notice that the automatic cleaner, if you have a suction side cleaner, is moving extremely slow in the pool. This also is the same for a sand filter. When the PSI gets about 30 or 10 PSI above the clean mark, you're going to notice a serious circulation problem with the sand filter. Now, the only filter that really isn't affected by getting impacted by dirt is a larger cartridge filter. Anything over 300 square feet on an average sized pool. Now you can also have an undersized filter based on how big the pool is. I'll go over that as well. But I'm using 15,000 gallons as an average size pool. You're not going to have a serious impact on a cartridge filter. If you're like in Arizona or the high desert, you get a lot of windstorms or a lot of dirt that may impact the cartridge filter. But in a normal area, a normal amount of dirt and debris does not impact a larger cartridge filter as badly as it would a sand and D filter. Now, the nice thing about the sand and DE or diatomaceous earth filter is that you can actually backwash those and kind of get a fresh start and you know start over basically with a semi-clean filter just by backwashing it for one or two minutes. This is something that you'll learn out there. Sometimes you get to a pool and you notice that the pump doesn't really have a lot of water in it. It's like half full of water, half full of air, the pool's not circulating well, and then you simply backwash the DE filter for a minute and a half, recharge it with some DE, and you'll notice that the pump fills up with water, that the pool is flowing and circulating well. Because again, the key here is not just filtration with the filter, but also circulation. And I think that's something that you really need to remember when you're sizing filters that you're not just basing the size of the filter on filtration capacity, but also circulation capacity. So the other part of the question is: is the size of the pool important to filter sizing? And of course, it's critically important to filter sizing based on the size of the pool, how many gallons of water is in the pool. We'll determine what size pump and what size filter you'll put on the pool. Interesting enough, for a sand filter, the higher horsepower pump is not necessarily better for a sand filter. In fact, it's actually worse for the sand filter, because the sand filter actually is more effective with lower circulation than higher circulation, and it makes logical sense because basically you have you know 300 pounds of sand in there, and the higher circulation isn't going to necessarily clean the water. The larger sand filter will help with circulation. So putting a three-horsepower pump on a 300 pound sand filter will not necessarily increase the circulation, it may even have the opposite effect in that case. So the only filter type that I would say that a larger horsepower pump has a detrimental effect on would be a sand filter. Typically, one to one horsepower, one to one and a half horsepower is the pump that you're going to find in the sand filter. And for a large cartridge filter, if you had a 500 square foot cartridge filter, having a three total horsepower pump would definitely benefit that pool because you have such a large filter. Now, the gallons of water again are important. So for a 15,000 gallon pool, I think a three or four hundred square foot cartridge filter is sufficient. A three or four hundred pound sand filter or a 60 square foot D filter would be fine for that size pool. As you go up in size, I think you should really gravitate towards a larger cartridge filter the larger the pool gets. For example, I had a pool on my route that was about 40,000 gallons, and it had two 520 square foot clean and clear plus filters attached to it, which is about a thousand square foot of filtration area. And that pool never had any problems with algae, problems with the water clarity, because it had a thousand square foot of filtration area, and you can install equipment with filters in tandem to increase. Now you have to plumb these in correctly, of course, to increase the square footage. You can also buy larger square footage cartridges. I think Pinter has one that's over 600 square feet, and other manufacturers like K-Word has one that's 700 square feet. It's a commercial type cartridge filter. So you can definitely get away with one large cartridge filter, but I would say that anything over 20,000 gallons, I would shy away from sand and DE and just focus on getting a really large cartridge filter or maybe two cartridge filters in tandem. So what you're really trying to achieve with the filter sizing, in my opinion, and I've been harping on this the whole podcast, is circulation and not just filtration. And of course, the bigger the cartridge filter, the bigger the D filter. By the way, you can get quad D filters that are 100 square feet, which I really recommend the quad D filters for a lot of reasons, but you could also get a larger D filter with a quad Pentair quad D filter, and again they have 100 square foot, which definitely is sufficient for a lot of larger pools. And then of course a 400 square foot 400 square foot, 400 pound sand filter is pretty much a 450-pound sand filter, or 500-pound is pretty much a pretty huge sand filter and should fit the needs of larger pools. It's the same thing with cars. If you had a Ford F250, which is that gigantic pickup truck, you wouldn't put a four-cylinder engine in there. It probably wouldn't do much for it. You may be able to get up to speed, like you know, 0 to 16 in like 15 seconds. But that thing has a you know a 7.3 liter Godzilla, they call it V8 engine in there, and that's to give it that power. And the same thing with your pool, if you're putting a small little filter on a large pool, you're going to have problems with it even being able to circulate the water properly. And I can also correlate this with those above-ground in-text pools you order, and a lot of people get these 8 or 10,000 gallon above-ground pools, and the little filter that's included is like a 25 square foot cartridge filter. A lot of reasons why they do that is because the packaging, they can't put a 200 square foot cartridge filter in there and give it to you at the store and expect you to get it to your house. So they put a tiny filter in there with the thought of you probably upgrading that filter eventually. And if you've ever had an above-ground pool with a 25 or 50 square foot cartridge filter that's 10,000 gallons, you know how impossible that is to keep that clear. And the same concept goes for a 10 or 15,000 gallon in-ground pool. You would want to have a larger filter to increase the circulation to eliminate a lot of water clarity problems and other problems associated with that. And bigger is better in just about every single case. The bigger the pool filter, the more gallons of water you have, the bigger you have to go with that, of course. But a small pool with a bigger filter works much better and more efficiently than a small pool with a small to medium filter, in my opinion. And if you're looking for other podcasts, you can of course find those on my website at swimmingpoollearning.com. On the banner, click on the podcast icon. There'll be a drop down menu of over 1800 podcasts for you there. And if you're interested in the coaching program, you can learn more at poolguidecoaching.com. Thanks for listening to this podcast. Have a rest of your week and God bless.