Best filter for koi pond

Koi fish can create quite a mess, which is why having a reliable filter is crucial. It helps keep your pond water clean and maintains a healthy environment by balancing the chemistry.

Choosing the right filter for your koi pond can be tricky. But don’t worry, I’ll guide you through everything you need to know to find the perfect filter for your pond setup.

In addition, I’ll review five of the best koi pond filters available in the market today. This will make it quick and easy for you to get a new filter for your pond.

Ultimate Buyer’s Guide: Choosing the Perfect Filter for Your Koi Pond

Not all koi pond filters are the same. Different filter systems work better or worse depending on the style of pond you have.

Let’s take a closer look at some important features to consider when choosing a koi pond filter. This will help you determine the best option for you and your fish.

Filtration Stages

Every koi pond filter has two stages: biological filtration and mechanical filtration. These stages are essential for keeping your koi healthy, but they work in different ways.

Biological Filtration

Biological filtration is about dealing with biological waste, like ammonia, to maintain the water chemistry of your pond. It also helps to get rid of unwanted microbes.

In biological filtration, a special substance is used to encourage the growth of helpful microorganisms on the filter. These microorganisms convert the waste produced by your koi (ammonia) into nitrates, which can be used by the plants in your pond.

Biological filtration also includes using ultraviolet (UV) light to kill off harmful microbes, such as parasites and bacteria that can harm your koi.

If your filtration system has a UV light, keep in mind that its effectiveness depends on the clarity of the water and the speed at which it passes through the filter. The longer the water is exposed to the UV light, the better the treatment.

So, it’s important to consider the flow rate of your pump when using a UV light.

Mechanical Filtration:

Mechanical filtration is simpler than biological filtration, but it’s just as important. It uses a physical filter to remove particles like large bits of food waste and algae from the water.

Ideally, your filtration system should have multiple layers of mechanical filters in different sizes. This way, it can collect a wide range of particles without getting clogged.

Determining Optimal Filtration Requirements

The adequacy of filtration for your koi pond hinges upon two key factors: the pond’s dimensions and the fish population it accommodates.

Filtration systems are assessed based on their water volume handling capabilities, making it an ideal starting point. However, the presence of koi fish necessitates a higher filtration capacity compared to an unoccupied pond due to the waste and residue generated by these aquatic creatures.

As a general guideline, it is advisable to select a filtration system that provides two to four times the filtration capacity of the pond’s volume.

For instance, if your koi pond encompasses a volume of 1,000 gallons, it is recommended to acquire a filter designed for a minimum of 2,000 gallons. In scenarios where the pond houses a substantial number of koi or is exposed to direct sunlight for prolonged periods, a filter with a capacity of 4,000 gallons should be targeted for the same 1,000-gallon pond.

It is crucial to note that the aforementioned calculation denotes the minimum filtration capacity required. When confronted with uncertainty or faced with a choice between filter sizes, it is always preferable to err on the side of excess filtration capacity rather than being inadequately equipped.

Pressurized or Non-pressurized Filters: A Comparative Analysis

When considering filtration options for your koi pond, an important decision to make is whether to choose a pressurized or non-pressurized filter. Each system offers distinct advantages and disadvantages that should be carefully evaluated. Let us delve into this topic in greater detail.

Pressurized Koi Filters (Bead Filters)

Pressurized koi filters, commonly referred to as bead filters, have gained significant popularity among koi pond enthusiasts due to their versatility in pond design. These filters can be installed either above or below ground level and possess the capability to process large volumes of water.

One notable characteristic of pressurized filters is the slower water flow rate compared to non-pressurized filters. This attribute yields several important implications. The reduced water movement allows for enhanced overall filtration as the filtration media have more time to effectively cleanse the water passing through the system.

However, it is important to note that slow-moving water conditions can inhibit the growth of beneficial bacteria, which require an adequate supply of oxygen to process ammonia. This issue primarily arises in ponds with a substantial number of koi. Nonetheless, various measures can be taken to bolster the biological filtration process, such as incorporating a pre-filter or air bubbler into the filtration system or introducing activated carbon to the biological filtration media.


  • Suitable for above or below ground installation
  • Capable of handling substantial water volumes
  • Facilitates efficient filtration due to slow water movement


  • Oxygen depletion can hinder biological filtration (especially in larger koi ponds)
  • Higher cost compared to non-pressurized filters

Non-pressurized (Box) Koi Filters

Non-pressurized filters, also known as box filters, offer a simpler and more straightforward installation process when compared to bead filters. However, the use of these submersible filters does impose certain limitations on the pond design, such as depth restrictions and the necessity for a flat bench to support the filter.

The primary advantage of non-pressurized filters over bead filters lies in their ability to maintain the flow rate of water from the filter pump. This ensures that beneficial bacteria, thriving on the filter media, have an ample supply of oxygen, enabling them to function efficiently even in densely populated koi ponds.

Furthermore, the higher flow rates in non-pressurized filtration systems aid in self-cleaning of the biological media, as the flowing water dislodges any dead bacteria. Moreover, the increased flow rate does not adversely affect mechanical filtration.

While generally not required in most ponds, it is possible to employ a non-pressurized filter as a pre-filter in conjunction with a bead filter. This approach combines the advantages of highly effective biological filtration from the non-pressurized filter with the slow, high-volume mechanical filtration provided by the bead filter.


  • Easy installation process
  • Effective biological filtration
  • More cost-effective than bead filters
  • Self-cleaning of biological media


  • Imposes limitations on pond design

In summary, the choice between pressurized and non-pressurized filters for your koi pond entails a careful consideration of their respective pros and cons. Factors such as pond size, number of koi, desired filtration efficiency, and budget should be taken into account to determine the most suitable filtration system for your specific needs.

An In-Depth Review of the Top 5 Filters for Koi Ponds: Enhancing the Aquatic Environment for Koi Fish”

Immerse Yourself in the World of Koi Fish: A Comprehensive Evaluation of the Finest Filters for Optimal Pond Conditions”

After Expanding Your Knowledge Base, Discover My Expert Recommendations: Unveiling the Elite Selection of the Five Best Filters for Koi Ponds

1) Oase BioSmart Koi Filter

Oase BioSmart Koi Filter

Pressurization: No Pond Capacities: 5,000 or 10,000 gallons Filtration Type: Biological and mechanical UVC Strength: Not applicable Outlet Size: 2.5 inches Dimensions: 30 inches x 22 inches x 16 inches Warranty: 3 years

This non-pressurized filtration system presents an excellent solution for ponds accommodating a significant number of koi, as it provides superior biological filtration.

The filter incorporates multiple biological media filters, each offering a vast surface area. Furthermore, these filters are divided into distinct zones to optimize the biological conversion of ammonia into nitrite, and subsequently into nitrate.

Maintaining the filtration system is a straightforward process, facilitated by a built-in cleaning indicator and a sludge drain. Cleaning the filter involves simply turning off the pump and lifting the sludge drain handles.

However, it is important to note that compared to other non-pressurized filtration systems, the installation process of this system may be less intuitive due to inadequate instructions. Additionally, this particular system does not include a UV filter to effectively eliminate harmful bacteria.


  • Biological filtration divided into multiple zones
  • Convenient cleaning through the sludge drain
  • Available in 5,000 and 10,000-gallon capacities


  • Insufficient installation instructions
  • Absence of a UV filter

Buy it here:

2) Oase BioTec Screenmatic Koi Filter

Oase BioTec Screenmatic Koi Filter

Pressurization: No Pond capacities: 18,000 or 32,000 gallons Filtration type: Biological and mechanical UVC strength: Not applicable Outlet size: 3 inches Dimensions: 31 inches x 23 inches x 21.5 inches Warranty: 2 years

The Oase non-pressurized filter system presented here is a considerable expansion upon the BioSmart filter, exhibiting a substantial increase in size and capabilities.

Featuring an enhanced foam design surrounding the filters, this system ensures a secure seal to prevent any water leakage from the filter box. Moreover, the sludge box has been enlarged to accommodate the significantly higher capacity of this filter system, enhancing its effectiveness.

A notable addition to this model is the self-cleaning module, which permits the adjustment of water flow to facilitate the separation of debris from the filters. Additionally, the incorporation of water level optimization significantly reduces the likelihood of clogs occurring.

Regrettably, Oase has not addressed the principal drawback of the BioSmart filter in this new and larger iteration, as the filter continues to lack an integrated UV light. However, it is possible to acquire an optional clarifier for this purpose.


  • Ample filtration capacity
  • Expanded sludge box
  • Multi-layered biological filtration
  • Water level optimization


  • High cost
  • Absence of UV filtration

3)Goplus Pressure Bio Filter (Budget Friendly Option)

Goplus Pressure Bio Filter

Pressurized: Yes Pond capacity: 4,000 gallons Filtration type: Mechanical, biological, UV UVC strength: 13 watts Outlet size: 1.5 inches Dimensions: 22 inches x 17 inches x 17 inches Warranty: Not applicable

The Goplus pressurized koi pond filter presented here provides high-quality filtration suitable for various pond systems.

The inclusion of a 13-watt UV clarifier in this filter is a notable advantage as it effectively eliminates harmful bacteria and parasites by utilizing the slow water flow. The canister housing features a user-friendly design, facilitating easy cleaning by unscrewing and granting access to all internal components.

It should be noted that, like many pressurized filters, this filter may pose challenges in terms of water oxygenation. In cases where the pond accommodates a substantial number of koi, the addition of activated charcoal to the standard filter media may be necessary.

While this filter is efficient and cost-effective, caution is advised regarding its build quality. There have been reports of manufacturing issues with the filter housing, resulting in leaks in numerous units.

Furthermore, it is worth mentioning that Goplus’s customer support has received significant criticism for their lack of responsiveness in addressing filter system issues. Moreover, the company does not provide a warranty for this product.


  • Incorporates a UV filter
  • Simple and hassle-free maintenance
  • Suitable for small ponds
  • Affordable


  • Inadequate oxygenation for crowded ponds
  • Filter housing prone to leakage
  • Absence of warranty and subpar customer support

4)Bubble Bead Filter XS-1000

Bubble Bead Filter XS-1000

Pressurized: Yes Pond sizes: Available in sizes ranging from 300 to 20,000 gallons Type of filtration: Mechanical and biological UVC strength: Not applicable Outlet size: ¾” Dimensions: 32” x 10” diameter Warranty: Not provided

The AST bead filter presents a highly efficient solution for filtration, boasting an unparalleled ease of cleaning when compared to other systems.

A simple backwash is all that is required to effectively alleviate pressure build-up in the system, eliminating the need for the removal or replacement of internal filters.

Furthermore, this backwash process is delicately performed to prevent disruption of the biofilm present on the biological filtration media.

The bead filter specializes in mechanical filtration, effectively capturing 100% of particles larger than 50 microns and an impressive 50% of particles down to 5 microns, thereby ensuring the clarity of your water.

It is important to note, however, that this filter does not incorporate a UV light for the eradication of harmful bacteria.

The filter is available in a wide range of capacities, accommodating pond sizes from 300 to 20,000 gallons. Although a warranty is not provided by AST, the company prides itself on delivering exceptional customer service.


  • Effortless backwash cleaning
  • Superior mechanical filtration
  • Versatile range of filter capacities
  • Excellent customer service


  • Absence of UV filtration
  • No warranty

5)Aqua Ultraviolet Ultima II

Pressurized: Yes Pond sizes: Available in 1,000, 2,000, 4,000, or 6,000-gallon capacities Type of filtration: Mechanical and biological UVC strength: Not applicable Outlet size: 1.5 inches Dimensions: 34 inches x 16 inches x 16 inches Warranty: 1-year limited warranty

The Aqua Ultraviolet bead filtration system has garnered significant praise among aquarists for its remarkable ability to address the issue of inadequate biological filtration commonly encountered with bead filters. This system incorporates a redesigned biological media filter, featuring a ridged substrate that maximizes the available surface area for beneficial bacteria colonization. Rigorous testing has confirmed its proficiency in ammonia transformation, even in non-pressurized filtration setups.

One of the notable advantages of the Ultima II system is its effortless cleaning process through a gentle backwash. With a simple turn of a valve located on the side of the unit, the backwash can be initiated without the need to open the system or disrupt the filtration process for more than a few minutes.

While the Aqua Ultraviolet brand name may imply the inclusion of a UV light in this filtration system, it is important to note that a UV light is not a standard feature. However, users have the option to add a UV light in-line with the filter if desired.


  • Highly efficient biological filtration
  • User-friendly backwash cleaning procedure
  • Comparatively affordable for a bead filter
  • Backed by a one-year warranty


  • Does not include UV filtration

Which Koi Pond Filter is Best?

Determining the optimal koi pond filter depends on your specific requirements. Our comprehensive analysis of filtration systems reveals distinct advantages and disadvantages tailored to various pond types.

In the realm of bead filters, the Aqua Ultraviolet model emerges as a commendable choice, ensuring uncompromised biological filtration. However, it is important to note that this filter is best suited for koi ponds within the capacity limit of 6,000 gallons.

For larger koi ponds, the Bubble Bead and Oase BioTec Screenmatic filters present viable alternatives, boasting user-friendly cleaning mechanisms. On the other hand, individuals seeking cost-effective solutions for smaller koi ponds will find the Goplus pressurized filtration system to be a budget-friendly option.

After careful consideration, the OASE BioSmart 10000 emerges as my top recommendation for the finest koi pond filter.

Koi Pond Filters Frequently Asked Questions

Should I consider incorporating a pre-filter?

In most cases, the existing mechanical and biological filtration system in your koi pond should be sufficient to maintain the health of your koi, rendering a pre-filter unnecessary.

However, if your pond is heavily stocked with koi, you might observe that the filter is unable to capture all debris, resulting in accumulation. In such circumstances, the addition of a mechanical pre-filter can significantly contribute to the cleanliness of your pond.

Alternatively, if you have concerns about inadequate biological filtration, it can be beneficial to install a non-pressurized filtration system as a pre-filter in front of a bead filter. It is important to note that this step is only essential for heavily stocked koi ponds.

How frequently should I clean my filter?

There is no universally applicable timeframe for cleaning filters, as it varies depending on the specific filter system and pond conditions. The most reliable method to determine when to clean your filter is to monitor the outflow from the system.

When you observe a noticeable decrease in outflow or a drop in pressure, it indicates that it is time to clean the filter.

If you have concerns about the cleaning process, you may want to consider selecting a high-end filter, such as those offered by Oase, which includes a built-in cleaning indicator.

Alternatively, performing occasional backflowing of a pressurized filter can help ensure that you never exceed the necessary cleaning interval.

What size of pump is suitable for my koi filter?

The pump you select should have the capacity to filter the entire volume of water in your koi pond within one hour. For instance, if your koi pond holds 5,000 gallons of water, a pump with a capacity of 5,000 gallons per hour or slightly higher should be used.

However, it is essential to consider that the flow rate of your pump can affect the pressure within the filtration system when using a bead filter.

Refer to the manual of your bead filter to ensure that you do not exceed the recommended pressure limit, as using an excessively powerful pump could lead to overpressurization and damage to your filter housing.

Final Thoughts

Choosing the appropriate filtration system is a critical aspect of establishing and maintaining a koi pond. With a high-quality koi pond filter, you can ensure that your pond water remains clean, the chemical balance is maintained, and your koi can thrive in a happy and healthy environment.