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Understanding Hot Tub Filter Systems: Which Is Best And Why?

Anytime you have a small, heated body of water, you want to make sure the proper standards are taken to keep it clean.

We all know about chemicals such as chlorine and bromine being used to sanitize hot tub water, but hot tub filter systems are just as important when it comes to water cleanliness.

Let’s dive into the wonderful world of filtration systems, so you can better understand them, and choose the right one for your tub. 

What Does A Hot Tub Filter Do?

A hot tub filter has one job: to remove debris and impurities in the water.

The ideal chemistry of the water is dependent on the proper levels of pH, total alkalinity (TA), calcium hardness (CH), and a sanitizer such as chlorine or bromine.

Chlorine/bromine is used to disinfect and kill viruses, bacteria, and pathogens in the water. But that’s all these chemicals do. The bad stuff is killed off, but now you have dead bad stuff in the water.

To remove these impurities, the tub needs to have a filtration system. 

As tub water is sucked in by the pump, it’s sent through the hot tub filter. It’s here where the dead viruses and bacteria collect. The filter then allows clean water to pass through it, cycling it back into the spa.

Types Of Hot Tub Filters

Now that you know what a hot tub filter does, let’s examine the filter media types so you can better understand how they remove contaminents from the water.

You’ll come across the following types:

Cartridge Filters

These are the most common filters you’ll find due to their ease of use, cleaning, and replacement.

Cylindrical in design, these filters use spun and bonded polyester, with continuous filaments for strength and efficiency. They’re also anti-ravel and fray-resistant with crisp pleats for added longevity and an increased filtration surface.

They can last anywhere from 12 to 24 months on average.

Ceramic Filters

Ceramic filters are similar to cartridge filters in both design and function, but they use a ceramic media rather than polyester.

This makes them quite a bit more resilient, outlasting any other filter media currently available.

Sand Filters

A spherical container which houses silica sand, this filtration system is more common with pools, but can also be used with hot tubs.

This filter uses silica sand because it’s spiky grain allows for contaminants to stick to it, while the clean water can continue passing through the sand.

Over time, these grains will break down and you’ll have to replace the sand somewhere between 3 and 5 years.

Diatomaceous Earth (DE) Filters

DE filters can remove water pollutants as small as 1 micron (translation: that’s really, really good), and are the option to go with if you want the cleanest water possible.

Cylindrical filter grids are housed in a container, and DE powder coats them. Pollutants then stick to the DE powder as the water passes through the filter.

DE filters last a long time, but they’re also expensive and require DE powder be added regularly to keep them in top condition.

Types Of Hot Tub Filtration Systems

Filtration systems refer to how the water is circulated out of the tub, sent through the pump, cleaned by the filter, and returned back to the spa.

There are two main filtration systems that hot tubs use – pressure side (the older technology) and suction side (newer technology). 

Pressure Side Filters

Pressure side hot tub filters emulate the filtration system of an inground pool. The filter for this system is housed in a dedicated canister and located after the hot tub pump in the equipment chain. This location is known as the pressure side of the pump.

A vacuum on the floor of the tub works with the tub’s skimmer to take in dirty water from the spa. This allows for both the vacuum and skimmer basket to pre-filter the water, catching large debris before it enters the system. This preventative measure protects both the pump and filter from clogging. 

Dirty water then goes through the pump, then through the filter, and the resulting clean water is sent back to the tub via its return jets.

Suction Side Filters

Suction side filters are what you will find in most hot tubs today.

This system works by placing the filter cartridge inside the tub’s skimmer, on the suction side of the spa’s pump. 

Surface water gets sucked into the skimmer and passes it through a filter basket. Then, it meets the cartridge filter which removes pollutants. The clean water is then sent through the pump, and gets returned to the spa via the return jets.

Pressure vs Suction Filters

The main difference is that pressure-side filtration occurs after the spa’s pump, whereas suction-side places the filter before the pump.

A suction side system is cheaper to install, which is why they’re so popular. But the trade off is in efficiency.

With only the surface water being sucked into this filter, it means heavy debris will fall to the floor and need to be removed by hand. Additionally, you have to run it for long periods of time – a minimum of 8 hours a day and sometimes over 12 hours. That will cause a big spike in your monthly bills.

Pressure-side systems are more expensive, but more efficient. You can filter the water a lot faster in only 2 to 4 hours, and the dedicated pump they use is more energy efficient than suction-side jet pumps.

Also, they excel where cleaning is concerned. The built-in floor vacuum sucks in heavy debris automatically so you never have to remove it by hand.

As they keep the water impeccably clean, you’ll save on using products like clarifiers, or even draining the tub due to an influx of total dissolved solids (TDS)

Hot Tub Filter System Circulation

There are two types of pumps you can use with your hot tub: jet pumps, or circulation pumps.

Standard Jet Pumps

Jet pumps are significantly larger when comparing the two in size. The reason for this sizable discrepancy (see what I did there?) is due to how the pump operates.

It turns on once or twice a day to cycle the water and keep it warm. This pump only needs to run for a few hours, as it has plenty of power to get the turnover done quickly. The thermostat notifies the pump when there’s a temperature drop in the water. The pump then turns on, running water past the heater.

The downside of this pump is that because it’s larger, and works to restore heat to the water, it uses up a lot of energy, and as a result, your electrical bill goes up.

Additionally, if it breaks down it’s a more expensive pump to repair and/or replace. You’ll also have to drain the tub completely when working on it or swapping it out.

Pros:

  • Provides a lot more power than a circulation pump
  • Can turnover the water faster than a circulation pump

Cons:

  • Uses up a lot of energy
  • More expensive in repairs, replacement, and monthly bills

Circulation Pumps

Where jet pumps are about the size of your forearm, circulation pumps (circ pumps) can fit easily in the palm of your hand.

They work by constantly circulating water throughout the day, drawing it past the heater and filter non-stop. They operate at a lower speed than jet pumps, and the continuous water cycling provides you with around the clock filtration.

Their low speed creates a smaller draw of water, which means they don’t use as much energy, and you’ll pay less for your monthly electric bill.

Circ pumps are also more affordable than jet pumps, quieter, last longer, and can be replaced without having to drain the tub.

Pros:

  • Keeps water cleaner than jet pumps with 24/7 circulation
  • Energy efficient choice for lower electricity costs
  • Less expensive to repair/replace

Cons:

  • Not as powerful as jet pumps
  • Needs to run non-stop (jet pumps run only a few hours)

Jet Pumps vs Circulation Pumps

For the most part, circulation pumps are the clear winner between these two.

Jet pumps are great if you have a large body of water that needs to be cleaned quickly. But their downfall is that they’re pricey and do a less effective job sanitizing the water. 

Circ pumps provide more benefits to your tub and wallet – cleaner water and less strain on your bank account at the same time.

Other Hot Tub Filtration Questions

Here are a few questions you may be asking yourself when it comes to hot tub filtration.

Does The Filter Size Matter?

Filter size does matter in the sense that a bigger filter will provide you with more longevity. However, the flow rate and turnover of the water will be the deciding factor of this.

A 25 square foot filter is usually more than adequate for most hot tub sizes, and some even get as large as 75 square feet. 

How much water is going through the filter, and how often, will determine how many impurities come out of the tub.

Does The Number Of Filters Matter?

In a single word, no. 

It doesn’t matter if you have 1 big filter, or 5 small filters, the amount of filtration will be the same.

Multiple filters in a hot tub is known as “non-bypass filtration”, where the claim is that 100% of the water is filtered at all times because the tub is outfitted with so many filters. They won’t miss a single drop!

But water filtration doesn’t work that way. As soon as you enter the tub you pollute it. After water is filtered, it’s sent back into the tub, which is simply mixing freshly filtered water with the dirty tub water. It will take hours for the filtration system to restore the water to a 100% clean state.

The only way you could filter out 100% of the debris floating in hot tubs, is to fully drain the water while filtering it, and then fill it back up with the filtered water. And obviously, that’s just ridiculous.

How Often Should You Clean The Filter?

Cleaning your hot tub filter is easy to do, and you should be inspecting it a minimum of every 2 to 3 weeks. 

Over time it will pick up a lot of debris, so working this into your maintenance schedule will keep it operating at its highest level.

Most of the time you’ll only have to rinse off the cartridge with a garden hose, but filters that have been used for 2 to 3 months will need chemical soaks to remove more stubborn debris. At the 1 year mark, you should replace the filter.

A Filter System Is The Beating Heart

There’s a lot to digest when it comes to hot tub filters, as well as the pumps used in their systems.

The bottom line is that even the most minimal filtration system is still pretty good. Understanding the nuances of how these systems work can help you decide on one that will do an excellent job cleaning your tub for the least amount of money.

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