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Fish Care to Maintain Water Quality

Fish Care to Maintain Water Quality

There are a few reasons why a pond goes from crystal clear to cloudy, smelly, murky, and even green. Excess waste, debris, and poor oxygenation cause most water quality issues, including algae blooms. It’s important to balance your pond with good bacteria and minimize debris in the water. If you have fish in your pond, they can contribute to the water quality problems if you’re overfeeding them or there are too many fish in the pond. Learn more about fish care to maintain water quality. 


Fish typically only eat until they’re full. The uneaten fish food sinks to the bottom of the pond and slowly breaks down. When feeding your fish, only give them as much food as they can in a few minutes, once or twice daily. Start off slowly. You can always give them more if they quickly eat all their food and treats. 

Fish need more food in the summer than in the winter, as they’re more active in warm water. By the end of summer, your fish are ideally looking plump and ready to transition into fall and live off their fat storage during the winter. 


A pond’s natural nitrogen cycle and filtration system can handle small amounts of waste. Fish naturally create waste, which is not typically problematic unless the ponds become overcrowded. If your pond has too many fish, they will quickly deplete the water of oxygen and produce more waste than can be broken down or filtered out. 

Give Your Fish Plenty of Room

When adding fish to your pond, knowing how big they will get is essential. The idea that a goldfish will only get as big as its container is a myth. Goldfish may appear to only grow to the size of their container because of stress and lack of resources or premature death. Some goldfish species easily grow up anywhere from 8 inches to over a foot long. Some koi can grow up to two or three feet long. 

Think About Adult Fish Size

When deciding which types of fish to get for your pond, the rule of thumb is generally that you need ten gallons of water for every inch of fish. When doing this calculation, estimate how large your adult fish will get. Many goldfish and koi you get from the store are only a few inches long and are babies or young adults. In a healthy environment, they will get much larger. 

What to Do if Your Pond is Overcrowded

If your pond becomes overcrowded, you can do a few things. You can make your pond bigger, add a second pond, or re-home some of your fish. Many local water gardening clubs reach out to each other to either give away or sell their fish. Never dump unwanted fish into local waterways, as they can quickly take over and disrupt the local ecosystem. Learn more about what to do when your fish grow too large. 

Oxygen Levels

Keeping your pond properly circulating and oxygenating is helpful for your fish and water clarity. Especially in the warmer months of the year, ponds can lose oxygen. Your fish and the beneficial bacteria that break down waste need oxygen to survive. 

Besides poor water quality, another sign that your pond lacks oxygen is if your fish are hanging out at the surface more than usual. You can keep your pond aerated with a water feature like a fountain, waterfall, or spitter, and a filtration system. Learn more about how to choose the right size pond pump.  

Water Quality Tests

Besides visible waste, fish also excrete ammonia into the pond. Performing water quality tests helps detect water quality issues that aren’t as obvious but can hurt water clarity when left unchecked and harm your fish, and cause illness. 

As a good rule of thumb, check your water at least once a month, ideally twice a month in the warm summer months, to make sure your water is balanced and there are no contaminants. You can buy water quality test strips at your local hardware or pet store, or some stores allow you to bring in water samples for testing. Read more about water quality and testing.

Water Treatments

smartpond water treatments are safe for ponds with fish when used as directed. Always follow the instructions carefully on each water treatment. Dosing instructions and product strengths vary from treatment to treatment. You can use many of these treatments to prevent issues before they start creating problems in your pond.

Fish are an excellent addition to a pond. They add color, movement, and life to your water feature. Fish make great pets, especially koi and goldfish, who are known for being social and will enjoy greeting you during feeding time. If you have a pond with fish, it’s important to focus on water quality for your fish’s health and to keep your pond water nice and clear. Overfeeding and overcrowding are the two main fish-related issues that can hurt water quality. When you focus on proper fish care to maintain water quality, you can have a clear pond and healthy fish.



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