Can a Pool Filter Get Clogged? and Why did it Happen?

Iron in Filter from Well Water

Troubleshooting issues with your pool can literally make you want to grab chunks of your hair out of your head. I’ve been right there with you! Let’s dive into checking out your pool filter issues.

Yes, a Pool filter can become clogged. It isn’t a bad thing if your pool filter becomes clogged because that means it is doing its job. The filter is catching many small particles and debris to keep your pool clean. Some pool filters will clog faster than others, and your pool filter clogging might mean you require attention to your pool maintenance to prevent the clogging from happening.

We are going to jump into some more information on how and why your pool filter might be getting clogged. This knowledge might help you prevent your filter from getting clogged so often in the future.

How a pool filter becomes clogged

A pool filter becomes clogged by doing a good job. Even though it’s frustrating for us pool owners to have to manually deal with these clogged filter issues at least we know that the pool filter is actually working. If your pool is surrounded by trees, pollen, or any activity that will kick up dust it’s not crazy that your pool filter will become clogged. It’s grabbing all of that nasty stuff and keeping it out of your pool water. 

The more annoying ways pool filters become clogged is by the stuff that we can’t see clearly with our own two eyes. This falls into the categories of algae, oils, and minerals. These smaller particles will really clog up a filter if you are having any of these issues.

At the end of the day, knowledge is power for us pool owners. If we are seeing these constant clogs coming up then we know that there is an issue that we need to resolve. Large debris issues might be out of our hands except for more diligent pool cleaning with a rake and vacuum. The smaller particles are going to require a deeper dive with some testing of your pool water most likely. 

How a DE, Cartridge, and Sand Filter Become Clogged

There are a few different types of pool filters out there like DE, Cartridge, and Sand Filters. These are listed most expensive to the least which also indicates how effective of a filter it is.  All of them can become clogged over time and will definitely become clogged if certain issues arise in your pool water maintenance. 

Since all pool filters are developed to catch debris, particles, algae, and many other contaminants they will keep these trapped inside the filter so they don’t get out into your pool. If your pool water is suffering from being very dirty because of poor chemical balance this is going to affect your pool filter as it’s going to be working overtime catching all of that debris and particles you don’t want in your pool. 

Sand Filters

A sand filter will trap the debris particles by collecting them inside the sand. Water can pass through the sand and come back out into your pool but the debris will remain behind inside the sand. The sand filter becomes clogged and less efficient over time as more debris collects inside the media(sand). This is when you’ll need to change out your media completely or pull some of the debris off the top of the sand and add in new sand. 

Sand filters are great at collecting large particles quickly but aren’t as good at collecting the smaller particles as quickly as other filters. If your pool is trying to recover from an issue with Algae, it will not clog as quickly as other filters because it doesn’t collect those tinier particles as quickly. Over time, if too much debris, oil, and small particles get trapped in your media it will need to be replaced with new sand.

Cartridge Filters

The cartridge filter pushes water through polyester fibers, it’s better at trapping large particles and some smaller particles. It would be normal to see your cartridge filter become clogged frequently if your pool is pulling many small particles into your filter at one time. An algae bloom can really clog up your cartridge filter quickly if your pool chemicals aren’t correct. The algae becomes trapped inside the polyester fibers in the cartridge and then hopefully killed by your chemicals. If you are suffering from some algae bloom then these cartridges are going to get filled up with dead algae rather quickly. Oils and Minerals will get trapped easily in a cartridge filter as well requiring special cleaners to get these particles out of the polyester fibers.

DE Filters

DE filters use Diatomaceous earth powder to trap small particles inside its grids. It can become clogged very quickly when dealing with things like algae because it does the best job out of all filters of collecting these small particles of Algae. This does mean it will become clogged much quicker and easier in comparison. This can cause you to end up cleaning out your filters often if you are having any types of problems with your pool water. Which can get costly because you’ll have to continue adding more DE Filter to the grids. 

A good note though is that a DE filter will get your pool water looking great if you are able to resolve the water maintenance issue. If you are able to kill all that algae with chlorine, the DE filter will trap the dead Alage quicker than any of the other filters.

Signs that your pool filter is clogged

There are going to be two major signs to look for to determine if your pool filter is becoming clogged. The first thing we will mention is your filter pressure rising from its normal pressure rate. If the pressure seems high, it’s time to backwash out your filter or manually clean out your filter. 

The second thing you can look for is a low return of water coming back into your pool. This can mean that the filter is keeping water inside and not pushing it back out into your pool at a decent rate. Just like above, you’ll want to backwash and possibly manually clean your filter. 

Pool Filter Becoming Clogged Quickly

If you noticed the signs that your filter was clogged, you probably took the steps to try and fix the issue. But quickly after you are getting the same issues popping up again. This is one of the most frustrating parts of dealing with filter clogs. The issue is probably going to be caused by the balance of your pool water but until you fix that you’ll have to continue to manually clean out your filters more than normal. It’s hard to determine exactly what the issue is causing your filter to clog but I do have some possible culprits. 

Algae Bloom is going to be the number one culprit on our list. Either your chlorine is not at a high enough level to kill off the algae completely or not at all. This means it’s coming into your pool filter and clogging it up repeatedly. The other option is that you are killing the algae, its becoming collected in the filter. If that is the issue then the clogging will continue to happen for a time but then should stop. If it doesn’t stop this means that the algae aren’t going away completely and you’ll need to test your pool chemicals to try and balance it out. 

Another issue that could cause some repeated clogging in your filter will be calcium. Calcium can cause the scale to build up into your filter not allowing water to pass through the filter efficiently. You’ll notice a hard scale build inside the filter and other parts of your pool if this is the case. Sometimes you can get this balanced out or you might have to do a complete empty and refill on your pool water.

Oils can be another culprit that is clogging your pool filter. These are easily cleaned out with certain cleaners meant to break up the oil out of your filter. If you suspect this is the issue, then a good cleaning with the correct chemical will help you get the oil out of your filter. You can also scoop out the top layers of your filter media in a sand filter. 


The founder of I wanted a place to share all of the great information from my family to other pool lovers, builders, and those looking to buy a pool.

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