7 Ideal Filter Systems for Koi Ponds & Small Water Gardens

New pond-keepers often wonder why they need a filter for their water garden. Natural ponds don’t have a filter, so why does a water garden need one?

Natural bodies of water usually have a source of running water, with either a stream or spring flowing into it. This helps to flush away nutrients and fish waste.

Best Pond Filter Reviews

There is also a natural balance between the level of fish, plants and billions of bacteria that control and recycle waste and maintain a nutrient balance.

The fact is, a man-made koi pond or water garden is not like a natural pond. Your pond is basically a hole in the ground lined with a water-proof plastic layer to keep the water from seeping out. It would never exist unless you built it.

Why do I Need a Pond Filter?

The idea behind having a pond is to bring natural aquatic beauty close to where you are, instead of having to hike or drive to experience it.

Because backyard ponds are completely man-made, they are dependent on us to make sure they are kept clean and healthy. A pond filter is a tool that helps us maintain the natural beauty of our man-made aquatic environment.

Think of it this way. If you built a waterfall next to your pond, would you expect water to automatically start flowing down the rocks? No. A pump is needed to bring the water out of the pond and to the rock falls. The same is true with water clarity. A pond filter is needed to keep the water clean and clear.

How to choose the right filtration system?

Selecting a pond filter can be a little confusing. We’ll take a look at the most common types of filters available for the typical backyard koi pond or water garden. There are pros and cons to every filter style. You’ll learn which kind of filter is right for your type of pond.

There is also the question of size. Filter manufacturers often rate their filters based on pond size (gallons of water). This rating is usually based on ideal conditions that favor clear, clean water.

In the real backyard pond world, the performance of the filter is affected by the amount of sunlight hitting the pond each day, the number of plants you have as well as the size, quantity and variety of fish you’re keeping.

All of these variables make it difficult to select a pond filter when you’re just looking at the “gallons treated” on the filter box. Filter manufacturers have entered a “gallons war.”

Pond filter capacity is often over-stated in order to appear to work better than the other brands. We’ve developed a way around this dilemma.

  • Cut the stated filter capacity in half for filtering a water garden or goldfish pond. Example: A filter rated for 5,000 gallons works best on ponds up to 2,500 gallons.
  • If the pond is in direct sunlight all day or if it is a koi pond, reduce the capacity by 75%. Example: A filter rated for 5,000 gallons would really be recommended for ponds up to 1250 gallons.

A pond filter needs a pump to supply it with a constant supply of water. The pond filter may come with a water pump. If you already have a pump, it may be too large or small for the filter. Check the recommended pump flow rates of the filter you are interested in. You may have to buy a pump that is matched to the filter. The filter manufacturer will recommend the correct flow rate for the filter.

A Word About UV Clarifiers

UV clarifiers work great for keeping suspended green algae under control. The algae cells are killed as they pass by the UV light. Algae are never completely eliminated in the pond, so the UV keeps killing the algae as it grows back.

Always use a pond filter with a UV clarifier. Without a filter, the dead algae cells fall to the bottom of the pond and form a messy sludge layer. The filter will capture the dead algae and keep the pond much cleaner!

We’ve looked at the different types of pond filters suitable for the average backyard pond. All of these filter catagories are available in different sizes, giving you many options to choose from.

Here are a few top rated pond filters to help you make an informed filter selection for your own pond.

Top-rated pond filters list

1. OASE BioSmart Pond Filter

The BioSmart gravity filter system uses multiple stages of mechanical and biological filtration system in a compact external filter box.

The filtration system is designed for medium-sized ponds with a moderate fish population.

The manufacturer rates the filter for ponds up to 5,000 gallons. It is not suitable for a heavily stocked expert koi pond.

Pond water is channeled through a series of filter foams that will culture beneficial bacteria. The filter system also acts a settling chamber. The water flow slows as it passes around the foam pads. Heavy debris falls to the bottom of the filter box. This helps reduce clogging of the filter pads.

The BioSmart system has a special filter cleaning mechanism that squeezes out the foam pads without having to remove them. Just raise and lower the filter pad handle several times. Dirt and debris is flushed away through a separate sludge drain. No need to remove the filter pads, just rinse out the filter box.

The stepped hose barbs accept hoses from 3/4” to 1 ½”. OASE recommends the AquaMax Eco Classic 1900 or AquaMax Eco Premium 2000 pump for this filter. The filter measures 23 x 16.1 x 19.1 inches.


  • 2-inch sludge drain for easy cleaning of the filter box.
  • Built-in foam pad cleaning mechanism.
  • Dial indicates when it is time to clean the foam pads.
  • Solid construction.
  • Easy installation.


  • None.

2. Laguna Pressure Flo Filter

The Laguna Pressure Flo series provide mechanical, biological and ultraviolet treatment of the pond water.

The filter is a sealed canister design, meaning it can be placed next to the pond or partially buried near a waterfall.

Water is pumped into the filter by your submersible water pump. Debris is captured inside the filter.

An indicator shows when the filter needs cleaning. The cleaning process involves raising and lowering the cleaning handles while opening a diverter valve. Dirty water is flushed from the filter and can be used as an organic fertilizer in your garden.

The filter has a built-in UV bulb that kills algae as it passes through the canister. Green water is eliminated, keeping your pond water crystal clear.

The Laguna Pressure Flo filters come with foam pads or lava rock.


  • Can be placed anywhere outside of the pond.
  • No disassembly to clean the filter.
  • Available in four sizes for ponds up to 4,000 gallons.
  • Uses quick-disconnect hose clips.
  • Kills algae.


  • Filter needs to be hidden from view.

3. Pond Boss Filter Kit with Pump

The Pond Boss internal pond filter is an easy to use filter for smaller ponds up to 500 gallons.

The water pump sits inside the filter box.

Water is pulled into the filter by the suction of the submerged pump.

Water is filtered through two layers of foam pads.

The first layer is coarse open-cell foam that catches large debris like leaves, plant stems and strands of algae. This protects the smaller pore foam pad from clogging too quickly.

The fine foam pad collects dead algae and smaller particles that cloud the water. The foam pads also protect the pump from clogging.

Plastic “bio balls” are included to provide surface area to aid in growth of beneficial bacteria.

The kit includes an ETL listed, energy efficient 320 GPH fountain pump. The fountain head creates an above-pond spray that is attractive and aerates the pond water.

The diverter valve is used to reduce the flow rate through the fountain head if necessary. The filter measures 12.25 x 6.25 x 7.


  • All-in-one pond filter kit.
  • Easy to set-up, just drop it into the pond.
  • Includes a water pump and fountain head.
  • Diverter valve is handy to reduce the flow rate.
  • 16’ power cord.
  • 1-year warranty.


  • Requires you to pull the filter out of the pond for cleaning.
  • Small filter surface area clogs sooner that wider submersible filters.
  • Fountain spray pattern can be blown by the wind.

4. Pondmaster 190 Pump and Filter with Fountain Head

The Pondmaster 190 pump and filter kit is similar in concept as the Pond Boss kit.

The Pondmaster includes a pump and fountain head but has some notable differences.

The filter system uses a reliable Danner 190 gph magnetic drive utility pump.

Water is drawn into a thick layer of open-cell foam which traps large debris like leaves and stems. A second layer of foam captures fine debris and acts as a home for bacteria, biologically purifying the pond water as it passes through.

The filter pads are larger (12” x 18”), which provides a greater filtration surface. This reduces clogging and allows the filter to run longer before maintenance is required.

The energy efficient water pump draws water through the filter pad then discharges through the bell fountain.

The fountain kit aerates the water and creates a beautiful, wind-resistant water pattern.

The filter measures 8½”x 10½” x 2½”. Rated for ponds up to 400 gallons.


  • Larger filter surface for better filtration.
  • Less clogging.
  • The filter handle makes it easier to remove from the pond.
  • Bell fountain head.
  • 10’ power cord.
  • 5-year warranty.


  • Larger dimensions take up more room in the pond.

5. Goplus Pressure Bio Filter

The Goplus Pressure Bio Filter is an external canister filter that sits outside the pond.

Pond water is pumped through the filter by your submersible water pump.

Pond water passes through layers of foam pads intended to capture coarse and fine debris. Plastic bio-balls are included with the kit.

The cleaning process involves opening a diverter valve to flush the canister. Dirty water is flushed from the canister. To clean the foam pads, you’ll have to open the canister and wash them manually.

The filter has a built-in UV-C bulb. Algae is killed as the cells pass by the UV. This is a proven method for eliminating green water algae blooms.


  • Rated for ponds up to 2,500 gallons.
  • Kills green water algae blooms.
  • Keeps pond water free of debris.
  • Canister can be positioned anywhere outside the pond.
  • Hose adapter for 3/4" 1" and 1 1/4" tubing.


  • Poor customer support.
  • Filter must be opened up to clean the foam pads.

6. TotalPond Complete Pond Filter with UV Clarifier

TotalPond’s pond filter is an external pressurized filter design.

The filter has a screw-on sealed lid that keeps the filter under pressure from the pump.

Gravity filters must be placed above the water level. However, the TotalPond filter can be place anywhere, even below the water level due to the pressurization.

Water is pumped from the pond and into the canister. Two layers of foam pads capture debris and will need to be removed periodically for cleaning. Plastic biological filtration balls are included.

This filter comes with an integrated 9-watt ultraviolet (UV) clarifier. The clarifier will kill floating algae cells as they pass by the UV light bulb that is encased in the water-proof housing. This helps keep the water clear without a green tint.

The TotalPond filter is recommended for ponds up to 1200 gallons. The manufacturer states that it can be submerged inside the pond too. However, this would make cleaning the filter difficult. The filter would be very heavy and hard to lift out of the pond.

The filter does not come with a water pump. The recommended pumps include TotalPond pumps: DD11560, DDUV800, LLUV1050, LL1200, LLUV1300, LL2000. The filter dimensions are 17.7” x 13.7” x 9.9”.


  • Economical pressurized pond filter.
  • Black color blends into landscape.
  • Includes a UV clarifier.
  • 16’ power cord for the clarifier.


  • Does not come with a water pump.
  • Requires two electrical outlets for UV and water pump.
  • Uses thin plastic that may not hold up well over time.

7. TetraPond Bio-Active Pressure Filter with UV Clarifier

This German-designed pressurized pond filter includes an ultraviolet clarifier.

Inside the filter Tetra’s plastic “bio-activators” serve as both debris removing and biological filter media.

Pond water flows down through the bio-activators which remove suspended debris and dirt from the water.

The plastic filtration media is unique to the TetraPond filter. The design of the plastic bio-activators provides a large surface area and unrestricted water flow to all the media for improved cleaning.

During normal filtration, the bio-activators capture dirt and debris from the pond. The extensive surface area allows beneficial bacteria to colonize for biological filtration. The filter can be back-flushed to remove dirt.

There are no filter pads to clog or change. During a back-flush, the bio-activators allow water to flush away sludge and debris.

The UV clarifier exposes single-celled algae to ultraviolet light as the pond water is pumped through the clarifier. The algae die and clump together and are removed by the bio-activators inside the pressurized filter.

Tetra Debris Handling Pumps are recommended for this filter.


  • Three sizes are available: 1,500, 2,500 and 4,000-gallon ponds.
  • Has a backflush feature.
  • Does not use foam pads.
  • High-quality construction.
  • Sturdy lid-clamps.
  • Complete instructions.
  • 2-year warranty.


  • More expensive than budget pressurized filter.

Types of Pond Filters

​Submersible pond filters

Submersible pond filters are the most basic type of filtration system. The filter consists of a flow-through box that holds foam or woven filter pads. Some models come with a submersible pump that sits inside the filter box. Water in drawn through the filter pads by the pump.

Filtered water is sent to a fountain or water fall. Just submerge the filter box and plug it in. The filter pads will collect debris like mud, plant pieces, leaves and sludge. Foam pads will remove some algae but not enough to clear up a green-water bloom. Some models include a few plastic biological filtration balls. The balls provide a place for beneficial bacteria to attach.

The truth is, all the surfaces of the pond, plants and the water provide plenty of space for bacteria and other microbes to grow. The bio balls are not really necessary.

Submersible filters are easy to install and require no plumbing work. Keep in mind that every time the filters get clogged, you’ll have to reach into the pond, pull out the filter box, disassemble the filter and rinse out or replace the filter pads.

Submersible filters are best suited for ponds up to 500 gallons.

External gravity-return pond filters

External gravity-return pond filters consist of a plastic box containing foam filter pads that capture suspended debris. The filter is positioned near the pond. Water fills the box, under pressure from your pond pump and then flows out of the box by gravity.

The filter box must be placed above the water level so water can flow back into the pond. Normally the filter uses two or more types of foam pads.

The best gravity filters use a coarse open-cell foam to capture larger debris followed by smaller pore foam pads to capture fine debris. The multi-porosity foam filters make the filter system more efficient and reduces the frequency of clogging. The filter pads are easy to remove and clean.

External filters are usually placed behind waterfalls or by the side of the pond. The challenge for some pond-keepers is finding a place to hide the filter.

Pressurized pond filters

Pressurized pond filters look like a small barrel with a tight-sealing lid. Water is delivered to the filter from your pond pump (under pressure), passes through the filter media and leaves under pressure. This means the pressurized filter can be placed anywhere outside of the pond. It can even be placed below the water level, at ground level.

Water will flow from the pressurized filter up to a water fall or water feature. Filter media is usually filter pads or special back-flushable plastic rings.

With some pressurized filters, you’ll have to open up the sealed lid and wash the media when the filter gets dirty. Advanced filter designs include a backwash feature that flushes the filter and rinses out the filter media without having to open up the filter.

Some pressurized filters include a UV clarifier that kills algae too. Pressurized filters will reduce the water pump’s flow rate by about 40%. You’ll have to over-size the water pump when using a pressurized filter system.

Some filter manufacturers also make water pumps and will recommend a specific pump for their filter system.

Final recommendations

If you have a small pond the Pondmaster 190 is an easy solution for keeping the water clear and aerated. The kit contains everything you need in one package. The high-quality water pump and bell fountain head gives you great value in a ready to use filter system. The filter handle makes it easy to lift the filter out of the pond for servicing.

If you’ve got a larger pond, the OASE BioSmart 5000 Pond Filter offers powerful filtration with easy maintenance. The external filter with the OASE cleaning systems makes maintenance a breeze.

For the most advanced filtration and algae control, the TetraPond Bio-Active Pressure Filter with UV Clarifier is our choice. This filter, coupled with a clog-proof Tetra Debris Handling Pump, will provide crystal clear water, algae control and easy maintenance. The bio-activator media never needs replacing and can be back flushed with a flip of a switch. This top of the line pressure filter is the ideal choice for larger water gardens and koi ponds.