Oxygen Preservation in Koi Ponds

When browsing through your local fish store’s medicine and testing aisle, you probably won’t find a test for oxygen. The importance of sufficient oxygen in your pond water is often understated, and misunderstood. While most fish owners understand the importance of low nitrates, did you know that low oxygen levels is one of the most lethal silent killers in the fish hobby?

The most common cause of low oxygen levels in a Koi pond is the overuse of algaecide. When it comes to treating algae with chemicals, more is NOT always better. In fact, as algae die off, oxygen levels in your water plummet. Most experienced aquarium and pond hobbyists can attest to the horror of treating for algae and finding your entire fish stock dead within an hour from asphyxiation.

Unlike nitrite, nitrate and metal poisoning, there’s no treatment for low oxygen levels once the fish begin to starve for air and experience stress. It can kill within an hour, and if you don’t catch it quickly (i.e. within the first 10 minutes), your fish usually have no chance of recovery. Fish suffering from low oxygen levels will start to linger at the surface of the water, usually gasping for air. After the first 5-10 minutes, the fish will lose control of their swim bladder and begin to struggle to stay upright. Within the next 45 minutes or so, internal damage to the vital organs occurs. Literally, the fish shuts down, fails to breath and quickly dies.

For every pond owner with Koi, preserving oxygen levels can be very challenging. You have a very large volume of water, and if you’ve planned it your pond correctly, you have several deep pockets of water. You’re more likely to struggle with oxygen levels in your pond true if you’re establishing a new system, or struggling with algae in an existing one. Luckily there are some easy inexpensive ways to keep oxygen level high in your pond to keep your fish happy and healthy.

The first tool to keep oxygen levels high is circulation. A lot of people have the perception that air bubbles or air stones will provide sufficient oxygen. While these air systems help, it’s not the action of the air bubbles rising from the bottom that provides oxygen. Instead, it’s the breaking of the surface of the water that allows oxygen exchange. When you have sufficient movement across the surface of the water, your oxygen levels will rise.

When treating for algae, this becomes even more important. Add an extra power-head to your pond when you use chemicals such as algaecide. Point the power-head up so you have plenty of surface movement. This simple step prevents the tragedy of losing your precious Koi to something preventable as low oxygen levels in your water.

Another commonly overlooked tool in increasing oxygen level is plants. Plants also help to naturally control algae! When you add plants to your pond, the plants compete with microbial algae cells for carbon dioxide consumption. Keeping your pond at least 1/3 covered in plants keeps your water clear and algae free. Best of all, plants help release oxygen into the water, which keeps your levels in balance. A great alternative to potted pond plants are floating plants such as water hyacinth or water cabbage. The most successful ponds contain lots of plants, which keep your water and your fish healthy.

Remember to conduct regular water changes for your pond, depending on your bio-load. Koi are messy fish, and if you have a fully stocked pond, you should aim for one 25% change per week. Water changes replenish oxygen and vital buffers that help keep your water stable. There’s nothing more helpful than regular water changes for your pond. Remember- if you take care of your water, your fish will generally take care of themselves because they will have a naturally supporting environment that fosters health.