Can I Use a Sand Filter on My DIY Hot Tub?

Can I use a Sand Filter on My Hot Tub

Can I use a sand filter on my DIY Hot Tub? This is one of the questions that I get asked a lot so in this article we are going to explore everything you need to know. I’ll let you into a secret, the answer is yes, but there are some exceptions.


This blog and my YouTube Channel have lots of info about building DIY Hot Tubs and Plunge Pools – if you have a question, get in touch.

Yes you can!


OK, so I am going to start with the answer and the rest of the article we will take a deep dive into sand filters. Yes, you can use a sand filter on your DIY hot tub however, your hot tub must have a plumbing setup that has a dedicated circulation pump.


Normally, you would have this kind of a setup if you were going for an Air Source heat Pump, Gas, Propane or any other external heating source that was not the electric from the Spa Pack.


The reason for this is all down to flow rates. Sand Filters are notorious in that they have very low flow rates. This means that if you try and put a dual speed pump though a sand filter on heigh you are not going to get the flow you need for your jets – there will be too much resistance.


Therefore, if you have a dedicated circulation pump, using a sand filter on your DIY Hot Tub is not a problem. But why would you want to do that? Let’s take a deep dive into everything sand filter related.


How Do Sand Filters Work?


Swimming pool sand filters work by using the principle of filtration through a bed of sand. The filter sand, which is made of a special type of sand that is specifically designed for pool filtration, is graded to a specific size and placed in the filter tank. The filter sand has a large surface area that provides a home for beneficial bacteria to grow, which helps to break down contaminants and keep the water clear.


When water is pumped from the pool into the filter, it flows through the sand, where dirt and debris are trapped. The clean water is then returned to the pool. The dirt and debris that are trapped in the sand are removed from the filter by backwashing, which is the process of reversing the flow of water through the filter and flushing out the trapped dirt and debris.


Sand filters are known for their low maintenance and durability. They are also relatively inexpensive and easy to install. They are typically used in residential swimming pools and smaller commercial pools. They are not suitable for large commercial pools or heavily used pools as they tend to clog up quickly and require frequent backwashing, which can waste water and energy.


It is worth noting that there are other types of filters commonly used in swimming pools, such as cartridge filters and DE (diatomaceous earth) filters. Cartridge filters use a replaceable cartridge that contains filter material. These filters are known for their ease of maintenance and require only occasional cleaning. DE filters use a fine powder made from the fossilized remains of diatoms, a type of algae. They are known for their high filtration efficiency and can filter out very small particles. However, DE filters require a high level of maintenance and need to be disassembled and cleaned regularly.


When choosing a filter for your swimming pool, it is important to consider the size of your pool, the number of users, and your budget. Each type of filter has its own set of advantages and disadvantages, and it is essential to choose the one that best suits your needs.

How does backwashing a sand filter work?


Backwashing a sand filter is the process of reversing the flow of water through the filter to flush out dirt and debris that have been trapped in the filter sand. Here is a general overview of the process:


  1. Start by shutting off the pump that is responsible for circulating water through the filter.
  2. Change the valve or control on the filter to the “backwash” setting.
  3. Turn on the pump, this will reverse the flow of water through the filter.
  4. Water will now flow through the filter in the opposite direction, causing the filter sand to move and the dirt and debris trapped in the sand to be washed out.
  5. The dirty water that is being backwashed is usually sent to a waste line or to a dedicated backwash holding tank.
  6. The backwash process typically lasts for about 2-3 minutes, or until the water coming out of the waste line or backwash holding tank is clear.
  7. Once the backwash process is complete, change the valve or control on the filter back to the “filter” setting.
  8. Turn the pump back on, and the filter will now be ready to filter the water again.


It’s important to note that backwashing should be done on regular basis, most commonly weekly or bi-weekly depending on the usage of the pool and the amount of debris in the water. Failing to backwash the filter regularly can cause the filter sand to become clogged, reducing the filter’s effectiveness and making it more difficult to clean.


How do you correctly size a sand filter for a swimming pool or Hot Tub?


Correctly sizing a sand filter for a swimming pool is essential for ensuring that the filter is able to effectively clean and filter the water in the pool. Here are a few factors to consider when sizing a sand filter for a swimming pool:


  1. Pool or Hot Tub Volume: The first step in sizing a sand filter is to determine the volume of water in the pool. This can be calculated by multiplying the length, width, and average depth of the pool.


  1. Flow Rate: The flow rate of the filter is the amount of water that the filter can process in a certain amount of time. The flow rate is typically measured in gallons per minute (GPM). The flow rate of the filter should be at least equal to the flow rate of the pump, and preferably slightly higher.


  1. Turnover Rate: The turnover rate is the number of times that the entire volume of water in the pool is filtered in a day. A turnover rate of once per day is considered to be the minimum, and a turnover rate of two or three times per day is recommended for a well-functioning pool.


  1. Size of the filter: Once you have determined the pool volume, flow rate, and turnover rate, you can select a filter that is appropriately sized for your pool. A general rule of thumb is to choose a filter that has a filter area that is at least two times the surface area of the pool.



It is also important to note that some sand filters have a maximum flow rate, you must make sure that the flow rate of your pump is not higher than the maximum flow rate of the filter.


What are the Advantages of Sand Filters?


Swimming pool sand filters offer a variety of advantages, including:

  1. Low maintenance: Sand filters are relatively low maintenance and easy to clean. Backwashing, which is the process of reversing the flow of water through the filter to flush out dirt and debris, is typically done on a weekly or bi-weekly basis.


  1. Durability: Sand filters are known for their durability and long lifespan. They are typically made of durable materials and can last for several years with proper maintenance.


  1. Cost-effective: Sand filters are relatively inexpensive and easy to install. They are an affordable option for both residential and commercial swimming pools.

  2. High Filtration: Sand filters are able to filter out dirt, debris, and other contaminants from the water, which helps to keep the water clear and clean. The filter sand provides a large surface area for beneficial bacteria to grow, which helps to break down contaminants and keep the water clear.

  3. Energy efficiency: Sand filters are relatively energy-efficient, as they do not require a lot of electricity to operate. The backwashing process is typically done manually, which eliminates the need for electricity or other energy sources.

  4. Compatibility: Sand filters are compatible with most types of swimming pools and pool systems. They can be used in conjunction with other types of pool equipment, such as pumps, heaters, and chemical feeders.




Whilst certainly less common on DIY Hot Tubs, it is possible to use a sand filter on your build. However, please make sure that you have a separate circulation plumbing setup and that the circulation pump you are going to use does not have a flow rate higher than the sand filter itself.


Happy Hot Tubbin’

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi


Hi, Andi here. I own and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi

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