What Is The Best Filter For Small Pools?
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What Is The Best Filter For Small Pools?
choosing the right filter for a small pool is more than just picking a piece of equipment — it can completely change how your pool looks, feels, and how much time you spend maintaining it. Many people assume that smaller pools are “easy” and that you can skim the surface and call it a day. The truth is, clarity and circulation are just as critical as in a 25,000 gallon inground pool. Get the filter wrong, or undersized, and you’ll find yourself chasing cloudy water, vacuuming every other day, and dumping chemicals like it’s a chemistry experiment gone wrong. I think that choosing the wrong filter and then dealing with the problems that this eventually causes is one of the most common causes for complaints and frustration with new pool owners...especially small pool owners as small pools.
In the small pool filtration world, three filter types dominate just like with larger pools: cartridge, sand, and DE (diatomaceous earth). Each comes with its own set of compromises and benefits. The right choice hinges on your pool’s volume, the type of debris it faces, and how much work you’re willing to put into maintenance. Fortunately there is a good bit of overlap from one filter to the next as to which pools can use them effectively but this article aims to improve upon this and dial in on the best filter options for small pools.
Cartridge Filters - My Go-To for Small Pools
For most small pools I work on, cartridge filters hit the sweet spot between performance and simplicity. There’s a reason I recommend them over and over. First, there’s no backwashing. That might sound minor, but every backwash is wasted water and wasted time - more and more areas have water restrictions and backwashing becomes a big problem. Cartridge filters capture particles down to 10-20 microns, keeping your water crystal clear while providing effective removal of debris at a wide spectrum of pool operating speeds and GPM. Cleaning is straightforward: every few weeks to every few months of operation, depending on your debris load, you pull out the cartridge, soak it in degreaser and hose it down (thoroughly) and it’s almost new again. Cartridge filters have extremely high maximum design flow rates making them suitable for modern (powerful) variable speed pumps. This makes cartridge filters the most energy and flow efficient filter option for pools large or small. It just so happens that with small pools this is a more important issue as small sand filters or small DE filters will have suitably low maximum designed flow rates...likely half or less what even small cartridge filters offer. Small sand and DE filters often can not handle the flow from the filtration pump in small pools.
Sand Filters - Easy, Low Cost and Functional
Sand filters still have a loyal following, and for good reason. They’re rugged, straightforward, and nearly bulletproof in terms of durability. Install it, backwash when the pressure rises, and for the most part, you can ignore it otherwise. For pool owners who don’t want to fuss with cartridges or DE, sand offers a “set it and forget it” style of filtration. Upfront, they’re often cheaper, which appeals to budget-conscious homeowners. We are talking as little as one third the price of a comparable cartridge filter!
Sand filters will work but they are not without their compromises. Sand isn’t as fine as cartridge or DE, usually filtering 20-40 microns, so very fine debris can sneak through leading to particulate being visible in the water, especially at night with the pool light on. Backwashing is necessary, which sends treated water down the drain — not a disaster, but worth noting if you’re environmentally conscious or dealing with local water restrictions or simply have no place on your property to deal with a discharge hose.
DE Filters - A Little Extra Work For A Lot Of Added Clarity
DE filters are regionally popular in some areas and completely absent in others. It is certainly worth noting that they have the most fine particulate removal ability of any type of pool filter option. They capture particles as tiny as 2-5 microns, far finer than sand and even slightly better than most cartridges. Properly sized, the filter cycles are long, and will require minimal maintenance in the form of stripping, cleaning and recharging with DE powder.
The catch? DE requires more diligence. You have to recharge the media, backwash carefully, and manage the disposal of spent DE. It’s not complicated if you understand the process, but it is more labor-intensive and involves working with DE powder regularly which I definitely prefer to avoid doing. For small pools where clarity matters — swim spas, plunge pools, or anyone who obsesses over sparkling water — it might be worth the effort but for most small pool applications I am going to go with a cartridge filter or a sand filter first.
Sizing Matters — Don’t Undersize Your Filter
Size is everything in pool filtration. Too small a filter doesn’t just underperform; it makes your pool maintenance experience miserable. You need to match the filter to your pump and plumbing to make sure that your filter can handle the flow your pump will be generating and pushing through it. Manufacturer flow specs aren’t suggestions they are for safety as well as for the longevity of your pool equipment. You should check the maximum designed flow rate for any filter you are looking to buy and then compare this to the performance curve chart for your pool pump to determine how much flow your pump will be generating, and whether your filter can handle this or not. This is one of the more challenging parts of sizing a pool filter and if you are not sure how to evaluate the flow chart / performance curve for your pump you might benefit from asking Steve for help.
Debris Considerations - What is the best pool filter?
Think about what actually ends up in your pool. Leafy trees, nearby construction, or even just a windy yard can dump fine dust and plant matter into your water. In-ground pools without covers collect leaves and organic matter due to massive amounts of old growth trees surrounding the pool...these are the pools that will be most worried about the debris load on their filter regardless of how small the pool is. Above-ground pools deal with splash-out and wind-blown debris. I tend to endorse sand filters for use in above ground pools and inground pools, even small ones, I recommend cartridge filters. This is purely due to the cost of cartridge pool filters being too much for above ground pools. The cartridge filter could cost as much as the rest of the pool kit put together!
I love cartridge filters but if you live in an area that gets absolutely loaded with organic debris, or swimmers by the dozen in your pool every day of the year...these high use and high debris load pools may be too much for cartridge filters resulting in having to clean them too often (weeks instead of months). In these pools an adequately sized sand filter might be the best option. So long as you have the availability to backwash a sand filter as often as it needs, this will definitely be the least work for you in terms of filter maintenance. For normal use and debris load pools, a well sized cartridge filter could go three to six months in between needing to be opened and cleaned. For many seasonal pool owners that can be the entire swimming year without a single cleaning being needed!
Cartridge filter sizing for any pool - Since cartridge filters all have such a high maximum design flow rate you can technically use almost any size cartridge filter on any size of pool. The only thing that changes is how long you will be able to go in between filter cleanings. The larger your cartridge filter, the longer you can go before you start to build pressure and need to open and clean your filters again. For example, for small pools I recommend (below) that a Hayward C3030 (325sf) cartridge filter is the best overall filter for small pools. It is the entry level size for quad element design. If you were to use the next size up filter, the Hayward C4030 (425sf) filter you would be able to go approximately 25% longer in between needing to open and clean the filter elements.
Pool Filter Maintenance
Whether you choose a sand filter or a cartridge filter for your small pool I can easily tell you the biggest problem pool owners will encounter with either. They will be good for a few months or a year or more even but eventually they all will develop a problem with oils. Both sand filters and cartridge filters require oil stripping as part of the regular cleaning. It's actually the most important part...and yet it is extremely common to find care instructions for these filters completely skipping this part.
When you clean a cartridge filter you need to soak it in a degreaser (filter cleaner) before rinsing. You can not just rinse the oils from the paper-like filter media. Similarly you should degrease a sand filter at least once per year. Most sand filter owners have never degreaser their filter! Use a sand filter degreaser chemical and follow the instructions on the bottle once per year. Removing oils from pool filter media is critical to the long term performance and effectiveness of your filter.
Pool filter degreaser
Type = Suitable for all filter types
My Filter Recommendation For Small Pools
Based on decades in the pool industry, my personal go-to for most small pools is a cartridge filter: reliable, efficient, and low-maintenance. A quad element cartridge filter is my favorite and these usually start in the 300sf range in terms of size. If you wanted the smallest possible filter and did not care about the quad element design the a single element cartridge filter like the Hayward W3C12002 still has a maximum design flow rate of 120 GPM despite being a single 125 sf filter element. For quad element the Hayward C3030 (325sf) cartridge filter which is one I endorse regularly or the equally comparable Pentair Clean & Clear 320. In the event that you would prefer a sand filter for your small pool then I recommend to stay around 250 to 300 pounds of sand, which is equal to about 24" tank diameter as this will have a more useful maximum design flow rate. For small pool sand filters I like the Hayward S244T2 and I like this sand filter due to the 2" connections and internal standpipe with a high maximum design flow rate (as far as sand filters go).
Hayward C3030 (325sf) Cartridge Filter
Max design flow rate = 122 GPM
Style = Quad element
Pentair Clean & Clear #160340 (320sf) Cartridge Filter
Max design flow rate = 120 GPM
Style = Quad element
Hayward W3C12002 Cartridge Pool Filter
Max design flow rate = 120 GPM
Style = Single element
Hayward S244T2 Sand Filter
Max design flow rate = 62 GPM
Style = Sand (300 pounds) with 2" connections
Pools Too Small For These Filter Recommendations
If you have a temporary pool or an above ground pool it is possible that your pool is simply too small to support these "small pool" filters that I have just listed. To address the disconnect here the pool itself needs to safely support the filtration equipment that will be running. A too-small pool, like a small above ground pool, was never intended to have a robust filtration system (pump and filter) attached to it, and doing so could likely create a dangerous entrapment hazard. This is why very entry level pools might not use the filters I have just listed. These pools would have to use the pump and filter that comes with the pool as it was designed to work within the (extremely low) flow limitations of the design. Small inground pools, surprising, will end up having filtration equipment almost identical to full sized inground pools simply because there are very few pool filtration equipment options specific for small pools. It is just an area of the pool industry where there is not a specific, targeted demographic of products.
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