Is Sand Good for a Koi Pond?

Koi Pond

Koi are majestic, large fish that are related to goldfish. They typically have a drab silver hue in the wild, but through generations of selective breeding, have produced colorful koi fish. Koi are hardy fish to be pet and can only survive in big outdoor ponds with filtration to maintain the water’s quality. One of the most common filters for a koi pond is sand, but can they keep the water quality acceptable for koi, and is it good for them?

Sand filters are a good and natural-looking choice for layering the bottom of a pond. Yes, it is good for your koi pond as it helps maintain the water at an acceptable quality. However, using it as a substrate for your pond presents several disadvantages. With sand as a substrate, you need to clean your pond regularly.

In this article, we will discuss the reasons why sand is good for your koi pond. We will also give you alternatives if you cannot use sand.

Click here to read our article: Can you use topsoil in Ponds?


Is Sand Good for a Koi Pond?

One of pond owners’ most common questions is whether they can use sand as a substrate for their backyard pond’s bottom. Sand is a good and natural-looking choice for layering the bottom of a pond. It is good for your koi pond as it helps maintain the quality of the water. However, using it as a substrate for your pond presents several disadvantages.

If you must, you don’t need to have a bottom drain and use sand for it. Most koi ponds remain healthier with just a bare liner at the bottom of the pond with no bottom drain. With sand as a substrate, you need to clean your pond regularly.

Here are the things to know when planning on putting sand in your koi pond.

  • Materials

Sand can make an appealing and pure statement at the bottom of your pond. It also provides a fresh and clean appearance. However, sand can be a heavy material that helps the pond liner stay at the bottom, where it must be. It can also clog filters and get in through the tears in the liner.

Some pond filters are designed to use and work best in the sand, but some others are not and don’t function well when sand gets stuck inside of them. Although, sand can get stuck in sand filters as well.

  • Bacterial Colonization

Bacterial colonization can happen whether you use sand as a substrate for other materials. Different types of bacteria can build in your pond, especially on the surface. Bacteria can ingest the pond’s waste, such as fish’s food and waste. It can also help your pond’s water be clearer and cleaner.

  • Waste Breakdown

Sand is composed of tiny rocks and mineral particles. These particles are too tiny to allow oxygen to get through them and discourages the colonization of beneficial microbes and bacteria. Not having any of these beneficial microbes in your pond can result in the pond’s waste getting rotten instead of being eaten and broken down.


How Sand Filters Work and Their Drawbacks

In ponds and aquariums, there are common types of filtration, one of these being biological filtration. This filter encourages the growth of the beneficial microbes or bacteria that break down fish detritus. Biological filtration plays an important role in the long-term health of your pond. Sand filters are just one example of a biological filtration with some mechanical attributes.

Sand filters force water upward through a bed of sand. This results in liquefaction, whereas the sand gets a hold of the liquid properties. When the particles of the sand suspend, their functional surface area increases, resulting in the encouragement of beneficial bacterial growth.

This helps break down ammonia, a nitrogen compound that koi fish release as biological waste. The beneficial bacteria then convert the toxic biological waste into less toxic compounds. Some commercial manufacturers of sand filters have screen filters that filter large particles and provide mechanical filtration as a secondary product.

Another yet less common sand filter that can be used for your koi pond and can be found at your local pet shops is the diatomaceous earth filter, which has silica sand and is made from skeletal microscopic planktons. This filter can clear your pond water quickly and produces exceptional mechanical filtration. However, diatomaceous earth filters don’t work at their best in ponds. Indeed, the level of mechanical filtration in a diatomaceous earth filter can result in clogging very quickly, making it best to use in an aquarium rather than a koi pond. If used in ponds, it can be a heavy chore since it needs hurley back-flushing due to the amount of debris.

Having a sand filter for your koi pond presents a few disadvantages. For one, the pumps in it might produce a loud, annoying noise as they force water through the sand. Sand filters require maintenance, back-flushing, and forcing water backward through the filter. This can prevent pond clog, which is caused by large particles in the filter. If your pond contains a lot of debris, it can represent a regular or daily task.


What to Put at the Bottom of Your Koi Pond

If sand isn’t a viable option for you to use at the bottom of your koi pond, we have alternatives for you. Although they don’t work the same way as sand, the following have their own advantages, which might better match your preferences.

  • Gravel or Small Rocks

This pond substrate with an eye-catching appeal defies the industrial look of artificial fish habitat. It also provides support for plants that aren’t kept in a container or pot. When choosing gravel or rocks for your pond, make sure to stir them regularly to prevent the rocks from cementing together.

This option is hard to clean since gravel and rocks collect lots of debris. If the gravel or small rocks substrate is deeper than 3 inches, your fish might be at risk of anaerobic bacteria buildup. Once these bacteria are cut off from the oxygen in your pond, they can create pockets of hydrogen sulfide, which can kill your koi or other fish.

  • Large Rocks

Another appealing bottom substrate for your koi pond is large rocks. Those are best for a pond with a river-like outlook. One of the disadvantages of large rocks is that they can be hard to clean as they are more likely to collect debris if you have them in multiple layers. Adding rocks at the top of a liner can cause erosion through the liner and require replacement.

  • Plastic Liner

A plastic liner is an easy-to-maintain and clean substrate option. It also works well with the bottom drain of your pond. When choosing a plastic liner, be aware of its thickness. A thinner liner may be cheap but will not last long compared to a thicker one.

A plastic liner isn’t aesthetically appealing compared to the other options mentioned in this article. It can create folds that might trap, harm, or worse, kill your koi. It can also be easy to tear from rocks, boots, and root growth.

  • Concrete with Spray Liner

A concrete bottom pond with spray-applied liner is easy to clean. It is also more durable than other simple liner ponds but can be an expensive option. Leakages and tearing are not a problem as this type of substrate works well in ponds, rocks, and boots.

However, this option might be prone to earthquake damages, and if it’s not properly mixed, can lose chunks of your pond surface, leading to leakages. Besides, with this substrate, you cannot alter or change the design of your pond nor add any underwater features.



Sand is a natural-looking substrate to use at the bottom of your koi pond. However, it is overlooked and controversial in the fishkeeping world. Sand and sand filters are great options if you are aiming for acceptable water quality for your koi and good bacterial colonization.

Now that you know the benefits of using sand at the bottom of your pond, you are well equipped to offer you koi the best fish environment. This low-maintenance option is great for koi keepers.

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