A filtration system is crucial for ensuring water quality in your koi pond. However, you can go further by supplementing your filtration system with a settlement tank.

A settling chamber will help eliminate waste and debris from the pond water. Here is what you need to know about adding a settlement tank to your pond.

Understanding How the Filtration System Works

Because a koi pond is a closed environment, things like fallen leaves, debris, uneaten food, and fish waste settle at the bottom of the pond. This organic matter decomposes and releases ammonia into the water.

Bacteria turns ammonia into nitrites during the first step of the nitrogen cycle. Then, another type of bacteria turns the nitrites into nitrates. Pond plants play an important part in this process by using some of the nitrates present in the water. You’ll also have to rely on bacteria to turn nitrates into nitrogen.

Nitrogen isn’t an issue as long as levels remain safe. However, a buildup of nitrogen in your koi pond is potentially dangerous to fish.

As a koi fish owner, you need to monitor the nitrogen cycle closely and establish a balance, so you have enough plants and bacteria for a healthy nitrogen cycle.

You’ll also need to use a filtration system to help remove some of the debris, ammonia, and nitrates from the water to supplement the natural nitrogen cycle.

What Is a Settlement Tank?

A settlement or settling tank is a component you can add before a pump pushes water through a mechanical filtration system or to supplement a biological filtration system.

As water goes through the settlement tank, waste, debris, and heavy particles will fall to the bottom of the tank. The purpose is to remove as much solid waste as possible before the water goes through the filtration system.

It reduces clogging and can extend the lifespan of your filtration system. And for those who rely on a biological filter, a settlement tank will make this filtration method more effective.

Pond owners typically use a sump pump to get rid of the waste that settles at the bottom of the tank.

How Do Settlement Tanks Work?

A settlement tank replicates a natural process that happens in all bodies of water. Waste, debris, and other particles sink to the bottom since they’re heavier than water. In a natural environment, these particles settle and become part of the substrate.

Koi pond owners typically use a 3 or 4” bottom drain to get water and debris out of the pump and into the settlement tank. As a general rule, the size of the settling tank should correspond to 10% of the total pond filter flow.

After going through the settling tank, the water will be cleaner and can go through the filtration system before a pump reintroduces it back into the pod.

Some settlement tanks have additional features:

• You can find tanks with aerators. This feature uses oxygen to oxidize some particles and make them heavier. It’s a useful feature to remove iron and other metals from the water.
• Some settlement tanks use a vortex motion to help particles settle at the bottom. A helix settlement tank can be more effective than a traditional rectangular tank.
• You can get tanks with additional features like microscreens that act as a mechanical filtration step. It’s a great way of catching waste and debris, but you’ll need to clean the microscreens regularly.
• You can also find tanks with mats that will catch smaller particles as water cascades through them.
• For larger setups, pond owners will sometimes create a second smaller dedicated koi pond with lots of aquatic plants and have it act as a settling tank.
• Another option for large ponds is to have more than one bottom drain take the water to different settlement tanks.

Do You Need a Settlement Tank?

Installing a settlement tank for koi pond is usually something you have to plan for when building a new pond since you’ll need to set up a bottom drain. While there are some benefits to using a setting tank, not every koi pond setup needs one.

You should think about using a settlement tank if you want to build a pond that uses biological filtration. The filtration process will work best if you can remove the bulk of the waste with a settlement tank. It will be easier to maintain a healthy nitrogen cycle and to have enough bacteria in your pond for biological filtration if you use a settling tank.

It’s also important to consider the size of your koi pond and how densely populated it is. Since the main benefit of a settlement tank is to remove fish waste from the water, it’s a component you should add if you keep a lot of fish in your pond.

There are additional benefits for those who live in areas with a warm climate. Things like direct sunlight, warm weather, and shallow water create perfect conditions for algal blooms. A settlement tank can help control nitrate levels to reduce algae growth.

A settlement tank can also be a good solution if you need to introduce some movement to your pond. You can increase oxygenation by removing a part of the water and reintroducing it into the pond, for instance with a waterfall. This type of setup can prevent issues linked to stagnating water, such as algae growth or a lack of oxygen in the water.