Hot Tub Filtration: Everything You Need to Know

By Jon Filson

Hydropool Hot Tubs and Swim Spas

Published May 15, 2024

When buying a hot tub, you’ll learn quickly that filtration is a key part of what you’re getting.

Water is wonderful, but it’s not pure. And a filter is required to remove particles of all kinds, from microscopic ones to bigger pieces like leaves and everything in-between.

Filtration is asked about when people buy at our retail outlets at Hydropool, with the questions coming in different ways. We get everything from “How does it clean?” to “To what microscopic level does it filter the particulate?”

In this article, we want to answer all those questions and many more. We want to explain:

  • The difference between filtration and sanitization.
  • How does a hot tub’s filtration system work?
  • What is filtered out in a hot tub?
  • What is the best filtration system?
  • What is Hydropool’s self-cleaning system?
  • How do I maintain my filtration system?

We hope that after this article, you’ll have a solid understanding of hot tub filtration.




What is the Difference Between Filtration and Sanitization?

This is key to understanding how a hot tub works to create water that is safe to use.

  • Filtration means capturing particles, including ultra-fine particles, that wind up in your water through a filter, which is essentially a mesh that traps the particles. It is entirely reactionary, in that the particles must first show up before the filters can do anything. The filter isn’t waving them away on top of your hot tub or anything like that.
  • Sanitization reacts to particles in the water and actively prevents them from forming. In hot tubs, it does this primarily through the bromine or chlorine you use.   

Together, these two processes work to keep your hot tub water as clean as possible.

A good hot tub filter is crucial in keeping you water safe for use. The one shown here comes with our Hydropool Signature models. Water is directed into the filter, through the below grate.


How Does a Hot Tub’s Filtration Work?

This will vary depending on the make and model of the hot tub.

Particles either sink to the bottom of water or float on top, due to the properties of water. You don’t see them floating in the middle: Over time the water places them in one spot or the other.

  • Particles that float on top are pushed towards what’s called a skimmer, which has a filter inside. The filter is made of a compressed mesh or some kind (anything from plastic to paper to fabric, sand, fiber or ceramic filters exist).
  • If you unfold the filter, it might be 25 square feet or it might be 50 – different manufacturers use different filter sizes. That’s why you may be looking at a filter that’s only 24” tall, but the manufacturer says it offers 25” feet of filtration.
  • Water is passed through the filter and matter is trapped in the folds.
  • The filter can be in the hot tub in different ways.
    1. Some of them are pressurized (such as Hydropool’s high-end Signature models). This forces all of the water into the filter, so that you can be sure all of it is being filtered. The con though is that unfiltered water runs through your pump, which is not ideal.
    2. Some of them are not pressurized (such as Hydropool’s Serenity line). They still clean your hot tub, they just take longer. Most hot tubs are in this category. The plus here is that the water is filtered before it goes through your pump, as the pump is located on the other side of the filter.
    3. As Hydropool shows by selling both, each option works.

Pressurized filtration comes standard with Hydropool’s Signature line of hot tubs. The pressure forces the water through the entire filter, making it actively clean it, rather than passively absorbing it in non-pressurized systems.

  • The filter removes the particles and holds on to them in your filter. It holds them forever, or until you rinse them out (this is why most manufacturers ask you to rinse your filter every week to 10 days or so). It’s also why you have to do a deeper clean on your filter every few months and why annually at least you have to replace it.
  • Some models will have a floor drain. This will also collect matter and direct it to your filter. (Hydropool has a floor vacuum on its Signature models, which actually pulls in the water in and forces it into the filter: this is a patented element unique to us as part of our self-cleaning system, which we’ll talk more about later).

This is a top-skimmer hard at work. Behind this mighty grill in a Hydropool Serenity model, lies a filter, which is actively removing particles from your hot tub’s water.

Do I Need the Biggest Filter?

Just like with insulation in a hot tub, you need sufficient filtration, not the most filtration. Some is good, more is better, but you can get more than you need. If you have 50 square feet of filtration in your hot tub and you’ve got a good circulation pump moving the water, you’ll have decent filtration overall.  

How Often Do I Change My Hot Tub Filter?

In most cases, we say once a year. But that will depend on usage. If you’re not sure on when to change your filter, here are a few guidelines:

  • You can always bring your filter in and show your local retailer who will tell you if it’s good or if you need to replace it.
  • If you see that it’s dirty and that it can’t be rinsed clean.
  • The water can hardly run through it.
  • Your hot tub water won’t balance easily or keeps having re-occurring issues. If that happens, one step in the process may be to change your filter.

What All Gets Filtered out in a Hot Tub?

Particles, let’s say. These include small pieces of skin, body oils, lotions, dirt, bacteria … everything that may or may not be on your body and everything that may or may not be in the air surrounding your hot tub that can drop in when you open the lid. That’s all what a filter is designed to catch.

Some systems have multiple filters, such as the Hydropool Signature Self-Clean system, shown above. The main filter (shown far above and in the cannister on the left in this picture) removes larger particles while the yellow-capped filter is more dense and captures smaller elements from oils and lotions.

What is the Best Hot Tub Filtration System?

Every manufacturer believes theirs is best. This is a competitive area amongst hot tub companies, although that has lessened over time as priorities shift.

For example, some companies have a system that forces the water up into the filter, some have multiple filters, some have a huge amount of filtration, some have cool names like “cyclonic filtration” – everyone has their own pitch.

How are you to decide?

  • If a company has been in business for a long time, chances are they have got filtration figured out at least so much that people don’t complain. That doesn’t mean it’s guaranteed to be great, but chances are it will be sufficient.  
  • Filtration is only one part of a process that involves cleaning your hot tub’s water. So if a company is coming on super-strong about its filtration, you may wonder about other cleaning elements.
  • What is ideal is that you have a solid understanding of the entire cleaning/sanitization/filtration system of any hot tub you’re considering and be confident that it works. Some customers aren’t like that, we understand, and you just want to buy with confidence. In that case, we recommend choosing a leading brand or one that focuses on this water cleanliness so you don’t have to think about it anymore.

What is Hydropool’s Self-Cleaning System?

We don’t want to be self-promoting in this article, but we do want to explain. If you want to know about Hydropool’s self-cleaning system, you can read more about it here.

If you want a quick understanding, here’s a video:

How Do I Maintain My Filtration System?

Again, each manufacturer will be slightly different, but in general:

  • You need to rinse your filter about once a week.
  • You need to soak it in a special cleaning solution once every few months that targets small particulate.
  • You need to replace it about once a year.

How Does Hot Tub Filtration Work?

Hot tub filtration is a core part of your hot tub. Without a hot tub filter, your water will decline rapidly. Particles can come from your body or from the air and all of those particles need to be filtered out one way or another.

We wrote this article to answer all of your questions about hot tub filters and we hope we have! If you have further questions though, please do not hesitate to reach out to your local retailer

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