Hot Tub Filter Systems 101 (Everything You Need to Know)

You’ve finally saved up enough money to purchase a new hot tub, or maybe you’ve installed a used one recently.

Maybe you purchased a home that came with a hot tub already set up, but you don’t know much about how it operates.

Or possibly you’re thinking of putting in a hot tub and want to know a little bit more about the type of work you can expect to do when you have one.

Whatever the reason, if you are looking for information about a hot tub filter system, you’ve come to the right place.

Hot tub spa filters can be a little bit confusing, especially if you’ve never owned a pool or spa before. Or perhaps you're still trying to figure out how to pick one? If you’ve ever operated an aquarium, you might know a little bit about how a tub water filter works. However, although the principle is more or less the same, the setup isn’t, so it’s a good idea to be sure you understand exactly what you’re dealing with before you ever purchase your hottub filter.

In this article, you’ll learn all about how to recognize the different types of filters as well as many different hot tub filter parts. You’ll know what a filter does and why it’s always important to have a filtration system set up in your hot tub. You’ll be able to perform a successful hot tub filter cycle from start to finish, and you may even be able to choose the right kind of filter or hot tub pre filter to suit your needs after you’ve learned about the varieties available, too.

By the time you’ve finished reading through this article, hot tub filter assembly and installation will feel like a breeze. The more information you have about this important part of your hot tub, the better off you’ll be, so let’s get started right away.

What is a Hot Tub Filtration System?

Before you go any further, it’s important to learn just what a hot tub filtration system really is. When you understand what this part of your hot tub is and how it operates in conjunction with the rest of your spa, you’ll be well on your way to successful installation, troubleshooting, and repair throughout the life of your filter.

To begin with, a hot tub filtration system is designed to filter water in your hot tub. This makes sense, of course, but what does that really mean? It means that the water used to fill your hot tub is passed through the filtration system before it ever reaches the tub portion of the spa. Most types of tubs must be filled through the filter in order to provide clean and comfortable water from the moment the hot tub is set up.

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The filtration system is usually installed inside your hot tub, with an access door in the tub portion of the spa through which water can flow easily. In some instances, the filter is installed outside the hot tub, and only the filter media is able to reach the water supply. Regardless of the type of installation your hot tub has, the filter more or less always works the same way.

When water is passed through the filter media, the filter catches a variety of different unwanted bacteria and other contaminants that are present in the water. The cleaner the filter, the better it works, so a brand new filter is more likely to catch almost all sediments, minerals, debris, and bacteria you don’t want to reach the tub of your spa. However, the longer your filter media is present in the water, the more build-up it will develop. This is why regular cleaning of your filter media is very important.

Unfortunately, sometimes the filter system itself can become damaged and need to be replaced. Regular maintenance of your filtration system can help keep this from happening, and it can also help you cut back on the amount of damage done to the rest of your hot tub throughout its life. Damage to the filter—and sometimes just a dirty filter cartridge or other media—can eventually lead to debris building up in and around your filter, too many bacteria in the water, or another problem that might cause pipelines, jets, and even the pump to wear down or break.

The filtration system is arguably the most important part of your hot tub. Read on to learn more about just what it does.

How does a Hot Tub Filtration System Help?

As outlined above, the hot tub filtration system has many important functions. Although briefly touched on in the previous section, here the benefits of the filter will be expanded upon briefly but thoroughly. Remember that it is always important to have a filtration system installed in your hot tub, and that operating the hot tub without a filter in place is potentially very damaging. Keep the following tips in mind to help you remember just how important and helpful a hot tub filtration system really is.

tub filtration system

  • Filters help keep bacteria from reaching your skin. As mentioned in the previous section, the media in any type of hot tub filter is designed to catch a variety of different bacteria before it’s allowed to enter the tub portion of your spa. Since hot tub water is very warm, it becomes a prime place for bacteria to thrive. In order to have the safest, cleanest water available to you at all times, you should always treat your hot tub with chemicals to achieve a safe and healthy balance, and you should never operate it without the filter in place
  • Filters can help large pieces of debris from entering your hot tub or your inner workings. Although you might assume you’d notice large items like sticks or leaves floating around in your hot tub water, when it comes time to turn on the jets and let the bubbles start moving through the water, you run the risk of missing items that might be in your water. If you sit in the hot tub with the jets on while something large like a stick is moving around in the water, you might end up getting cut on whatever that item might be. On the other hand, if that item gets sucked into the pipelines behind your filter, the entire hot tub system could easily be damaged.
  • Filters are beneficial for keeping air out of your pipelines. Like debris and large items, air is also an important factor in keeping your hot tub safe. While the air in your tub isn’t necessarily a problem, if it happens to make its way into the pipelines, you could have a big issue on your hands. Air in your pipelines can travel to the pump and cause it to operate incorrectly, which in turn might cause it to overheat or quit functioning altogether. With a filter in place, there’s much less chance that this could happen to your hot tub.
  • Filters make it easier for you to balance the chemical treatments in your water. Although the filter isn’t the only part of this important aspect of hot tub ownership, having a filter in place makes it easy for you to get the right readings on your water testing strips every time you test. It also makes it much simpler to treat the water with bromine, chlorine, or another type of chemicals you choose to add. When you have the filter in place along with a chemical treatment, the chances of unwanted bacteria in your hot tub are slim to none.
  • Many hot tubs simply can’t operate without the filter in place. Because of the importance of keeping air out of your lines and pump, many models of spas are designed to not function without the filter installed. In order for your hot tub to work the way it should, you will need to have a filter ready from day one. Without it, the water won’t be able to cycle through your hot tub properly, and although you might be able to fill the tub, it won’t be much fun to sit in.

Different Types of Hot Tub Filtration Systems

There are many different types of hot tub filtration systems available on the market today. Some of these are much more popular than others, but all of them are very much worth mentioning if you’re looking into installing a new hot tub or haven’t decided completely on the type of filter you want to work with yet. There are strengths and weaknesses behind each type of filter, so depending on what you’re looking for, you might want to choose one variety over another one to help best meet your needs. Familiarize yourself with each type of filter in order to make the best decision to suit your hot tub.

types of hot tub filtration

1. Cartridge Style

This is the most popular style of filter available, for a variety of different reasons. For one, these are very affordable filter systems, since many of them are made from plastic and include simple but effective cartridge media. These are usually larger filters that allow for plenty of surface area for water to pass through, which in turn means there’s a greater chance of water being clean when it reaches your hot tub. These filters are usually installed on the side of your hot tub, and water is allowed to flow through them before entering your tub. However, in some instances, they are attached to the outside of your hot tub instead.

type of filter on the market today

This type of filter is very good at what it does, and it’s able to capture a lot of bacteria and other contaminants. This type is also much easier to clean than any other type of filter on the market today. Since the cartridge can be easily removed, rinsed or soaked, and replaced as soon as it’s dry, this is a popular type of filter for anyone looking for a quick and simple cleaning process.

2. Diatomaceous Earth

cartridge filter

In essence, diatomaceous earth filters are a type of cartridge filter. However, they’re not exactly the same. While they are usually set up in much the same way as a traditional polyester cartridge filter, the material used for filtering your water is different. In this type of filter, diatomaceous earth fills the cartridge, and your water passes through this fine powder in order to remove as many bacteria as possible. This powder is made from the remains of diatoms that have been fossilized deep within the earth. This is a very prominent material found around the world, and its abundance makes these filters almost as affordable as traditional polyester cartridge filters.

3. Ceramic

part of filtration systems

Throughout history, ceramic has been an important part of filtration systems for many different groups of people. One of the most common and simplest forms of this type of filtration is the clay pot filter. Basically, in a clay pot filter, water is passed through a clay pot which catches much of the sediment and bacteria on its porous surface. The remaining clean water then drips through the surface of the pot into a container ready to receive it. Ceramic hot tub filters work in much the same way, although they’re a little more sophisticated and usually contain an extra level of activated carbon for more filtration protection.

4. Sand

 type of filter

This type of filter is growing more and more popular in recent years, particularly with hot tub and pool owners who are looking for a safer, less chemically-enhanced way to filter unwanted materials from their water. These types of filters are not quite as strong as some of the other varieties on this list, but they do a good job when combined with other forms of water sterilization. They are made up of large balls filled with sand that sit to the side of your hot tub. Water passes through the sand, which catches bacteria and debris along the way. As in a ceramic filter, the water that comes through the other side is clean and ready for use. This type of filter must be cleaned almost weekly, especially if you use your hot tub very frequently.

Parts of a Hot Tub Filtration System

Now that you know the different types of hot tub filtration systems available for you to choose from, it’s time to learn about the different parts that make up each of these. Although most types of hot tub filters work on the same principle, they have different parts, and it’s a good idea to know the difference between what you’ll be working with depending on the type of filter you end up choosing. Some filters have many different parts, while others have only a few pieces that work together to create a functioning filtration system. However, certain types of filters are much more expensive than others, so it’s up to you which one you think is best for your needs.

different types of hot tub filtration

1. Cartridge Style

A cartridge style hot tub filter has many different small parts. Some of these are more notable than others, but all of these parts are very important to the functionality of the filter.

  • Lock ring – This piece is at the top of a cartridge style filter unit. It is used to attach the filter to the rest of the hot tub. This is a small round piece that can be screwed into place in some models.    
  • Filter lid – The lid portion of the filter is designed to close as needed to keep water from entering, or open when necessary to allow water to pass through. It is made up of a few different pieces that combine to create this important feature.
  • Air vent valves – There are usually a few air vent valves involved in your cartridge style filter. These are in place in order to keep air from entering the filter, and in turn, from entering the pipelines throughout your hot tub. These are very important and should be checked periodically to ensure they are functioning as they should.
  • Cartridge – The cartridge portion of the filter is the part most people refer to as the filter itself. This is the media cartridge that you will clean and replace on a regular basis. This portion of the filter should slide into place in the entire filtration system. You should always purchase cartridges that are designed for use with your specific filter to be sure they’re the right shape and size.
  • Bypass valves – Like the air vent valves, these are in place for an important reason. They help water pass through the filter cartridge media freely every time you fill your hot tub.
  • Body – This is usually a long, cylindrical piece that holds the filter cartridge media, but the shape and size may differ depending on the type of filter you purchase.
  • Base – The base of the filter either holds the filter in place or attaches to another portion of the hot tub, depending on the model you’re using. It is usually a plastic piece that helps protect the bottom portion of the filter system.
  • O-rings, screws, and hardware – These pieces are important to the functioning of your filter cartridge, but you probably won’t have to worry about replacing them very often, if ever. They are simple hardware pieces that are present in just about any type of filter.

2. Diatomaceous Earth

Diatomaceous earth style filters are very similar to cartridge style filters, and many of the parts are the same as well. However, there are a few important differences which make this type of filter stand out.

  • Air release valves – Much like in the cartridge style filter, the air release valves in a diatomaceous earth filter are designed to let air out of the filter before it is pushed into the pipelines. They should be checked periodically to be sure they’re doing their job properly.
  • Body – Like in a cartridge style filter, the body of a diatomaceous earth filter is long and cylindrical in most cases. It is hollow and designed to hold the filter media. This makes up the bulk of the filtration system’s size.
  • Media – The media used in a diatomaceous earth filter is very similar to a cartridge, and in some cases, it may even be a cartridge. However, it is usually filled with a different type of material than that of a cartridge filter replacement. This piece slides into place inside the body of the filter.
  • Base – The base is, once again, usually a durable plastic piece that helps support the filter system and hold it in place in or around your hot tub.

3. Ceramic

Ceramic filters are also similar to cartridge style filters, but once again, they have a few differences. One thing to note is that there are far fewer working pieces involved in a ceramic filter than in a traditional plastic cartridge one.

  • Body – This is the large, cylindrical part of the water filter that holds the filter media. This piece is made of porous ceramic which is intended to sterilize the water before it is finished passing through the filter itself.
  • Filter media – Aside from the ceramic portion of the filter, the inner workings of this type of system also contain a type of filter media, which is usually activated carbon. This is the same type of filter present in a fish tank, and it is a great second level of protection when it comes to using water that passes through a ceramic filter.
  • Mouth – The mouth of a ceramic filter is usually threaded, which means it’s designed to screw into place in your hot tub. This may not always be the case, depending on the type of tub and model of filter you have. However, it should always contain some method of attaching it to the hot tub’s pipelines.

4. Sand

Finally, sand filters are set up fairly differently than the other three types of filters listed here. You’ll notice very different parts when working with a sand filter, but they still interact in much the same way.

  • Air valves – You’ve probably learned by now that air valves are an important part of any type of hot tub filtration system. The sand filter is no different. Once again, these valves are in place to let air leave the filter before the water pushes it into the pipes inside your spa.
  • Flange – This is basically an adapter that allows you to be able to install this type of filter on just about any model of hot tub. Some hot tubs still won’t be compatible, but with this adapter, you should be able to use this filter on most varieties.
  • Fill spout – This piece allows you to easily fill the hot tub through the filter without too much struggle. It’s always important to filter your water before it ever reaches your spa’s tub.
  • Pressure gauge – This piece keeps the pressure inside your sand filter from building up too high. It’s vital to the safe operation of this type of filter.
  • Filter basket – This is an important backup level of filtration that helps remove larger pieces of debris from your water as it passes through the full filter system.
  • Backwash adapter – This piece is important in that it helps keep dirty water from flushing back into the filter. You will need this adapter piece if your hot tub isn’t ordinarily designed for use with a sand style filter. More modern hot tubs, however, might not necessarily need it.
  • Hardware pieces – There are many different types of hardware pieces involved in setting up a sand filter. These small nuts, bolts, screws and pegs are important and should be checked about once a year as part of your regular hot tub maintenance. However, you likely won’t find yourself directly involved with them, since your filter will arrive with many of them already in place.

How to Assemble Hot Tub Filtration System Parts

Assembling your hot tub filter doesn’t have to be a scary and confusing experience. Although each filter and each hot tub are different, in this section, you’ll be provided with a simple guide to help you get started. This guide can be used to assemble a generic cartridge filter designed for use with most modern day hot tubs. All you have to do in order to alter this guide for other types of filters is to replace the different parts with the ones you have to work with. Remember that if this seems too difficult, however, you can always call the helpline for the company that makes your filter.

  • Remove all the pieces from the box. With most hot tub filters straight out of the package, many of the parts should already be put together for you, including several of the small hardware pieces.
  • Most standard cartridge filters will be separated into three parts when you remove them from the box: the base, the body, and the lid. The cartridge is a separate part, and any attachment rings or adapters will also be packaged separately.
  • Turn off the power to your hot tub and drain the tub. You can leave water in the foot bath if necessary while working on this job.
  • Position the base in place in your hot tub. In order to do this, you may need to remove the flapping lid or the grate protecting your filter. This is located inside your hot tub. On some models, you won’t have to remove this piece in order to access the filter housing unit.
  • Remove any existing cartridges that might already be in place. If you haven’t removed the old filter system, now is the time to do so.
  • Attach the base to the correct position inside the filter housing unit. Screw it into place firmly.
  • Attach the body of the cartridge into the base. This usually simply pops into place using an attachment gasket, but it might require a few simple tools in order to complete this step.
  • Slide the filter lid down onto the body of the filter. Once again, this should be able to be completed by hand, but in some instances, you will need to use tools to attach it correctly.
  • Place the new (or used but clean) filter cartridge media inside the body of the filter. This should be as simple as it always is to replace your filter cartridge media when it’s time for a deep cleaning. This step should be familiar to you if you’ve ever maintained a hot tub before.
  • Replace the door or grate to your filter housing unit if you had to remove it.
  • Attach your garden hose to the fill valve in your filter and fill up your hot tub as you normally would.
  • Turn the power back on to the hot tub and let it run a few cycles before you use it or proceed with treating it with chemicals.
  • Your filter system is now in place and ready to use.


As you can see, there is a lot to learn when it comes to your hot tub filtration system. If you’ve never worked with a hot tub filter before, you might feel more than a little bit overwhelmed by everything it entails. However, when you pay attention to the information listed above, you’ll be able to work with your hot tub filter in no time, and you’ll have a much better understanding of how it functions in relation to the rest of your hot tub, too.

In this article, you’ve learned a lot. You first learned what a hot tub filter is and how it benefits you when you have it installed in your spa. From there, you learned about the different types of filters available for you to choose from, as well as how to recognize the different parts that make up each of these types. Finally, you were presented with a walkthrough guide instructing you on how to set up and install a cartridge style filter, which can be easily adapted to any other type of filter you might choose.

You’ve come a long way since the beginning of this article. Now all that’s left to do is choose the right type of filtration system to suit your needs, and get out there and install it in your hot tub today. You’ll be able to soak in comfortable, clean, treated and filtered water in no time, and your hot tub will thank you for it.