Asked By: Jackson from Montpelier, VT
A: While koi fish can technically live without a filtration system, their lives will likely be shorter and lower quality than fish with filters. The same goes for a pond aeration system. Here’s why:
Why Koi Need a Filter
As fish eat and breathe, they release organic waste and toxic gases into the pond water. Leaves and debris in the water also decay and add to this waste accumulation. Without a proper koi pond filter, organic pollution will cloud the water, leading to muck and murk. This makes your backyard pond smelly and unpleasant for you, but it can become downright dangerous to your fish.
Koi fish in a dirty pond will spread disease like wildfire. Parasites, bacteria, and viruses can infect and kill your entire fish population without intervention. Additionally, minor abrasions can quickly become infected due to the unsanitary environment.
If koi cannot live comfortably without a filter, you may wonder how fish survive in the wild. Natural aquatic environments receive filtration through dense foliage and moving water from a spring or river source.
Fresh water flows into the pond, pushing polluted water to the edges and bottom of the pond, where plant roots can readily take up key nutrients. Plants consume excess nutrient pollution as fertilizer and convert harmful gases like carbon dioxide into pure oxygen. It can be challenging to plant your backyard pond dense enough to filter the water effectively, but a bog filter recreates this process with very little power needed.
Koi Pond Aeration
Just as filters are essential, aerators for koi ponds are vital for a thriving and healthy fish population. Diffused aeration imbues the water with life-sustaining oxygen, maintaining a cool and stable temperature and ensuring aquatic critters can breathe easily. Aerators also help clarify water and support beneficial bacteria colonies that microscopically filter ponds.
More Koi Pond Maintenance Tips
Still curious about how to filter a koi pond? Contact us online or call 866-POND-HELP to chat with an experienced pond coach ready to answer all your questions about koi pond care and maintenance.
Check out these related guides to keep learning:
Mechanical and Biological Filtration Explained
What is a gravity pond filter?
Last Updated: June 3, 2025