When it comes to pond care, there’s one issue that often flies under the radar: nitrates. At Envii, we think it’s time that changed. In this guide, we’re going to explain what nitrates are, how they get into your pond, and most importantly—how to reduce them naturally.
What Are Nitrates?
Nitrates are the final stage in the nitrogen cycle—a natural process that happens in every pond. Here’s how it works:
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Fish waste, uneaten food, and leaves break down into ammonia
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Ammonia becomes nitrites
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Nitrites convert into nitrates
Nitrates themselves aren’t toxic in small amounts, but too much leads to green water, blanketweed, and stressed fish.
Where Do Nitrates Come From?
Several everyday sources can increase nitrate levels in your pond:
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Sludge buildup from decaying organic matter
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Runoff from fertilisers used on nearby grass, plants or trees
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Tap water used in water changes (which often contains nitrates)
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Overfeeding fish, leading to excess waste
All of these add up over time—and without enough beneficial bacteria, nitrates can get out of control.
How Do Nitrates Affect Your Pond?
High nitrate levels fuel the growth of string algae and green water. If you’re battling algae, there’s a good chance nitrates are to blame.
Even treatments like Algae Klear Extra (which breaks down algae) can release more nitrates into the water. That’s why it’s crucial to test your water regularly using pond test strips that detect nitrates, nitrites, and pH.
Testing for Nitrates
We recommend weekly water tests. It only takes a few seconds:
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Dip the strip into the water
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Wait 30 seconds
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Compare the colours to the chart
In our recent test, we found our pond water had zero nitrates, with a healthy pH of 7.4—exactly where we want it.
How to Reduce Nitrates Naturally
You don’t need expensive gear—just smart pond care. Here are our top natural ways to reduce nitrate levels:
1. Control Sludge
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Use a pond net to remove leaves in autumn and winter
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A small amount of sludge is fine—it feeds plants
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But excess sludge = more nitrates
2. Avoid Overfeeding Fish
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If fish leave food behind, you’re feeding too much
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Fish (even goldfish!) can find natural food in the pond
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Less food = less waste = less nitrate
3. Add Plants That Absorb Nitrates
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Watercress (a bit of a rogue option, but powerful)
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Oxygenating plants, like hornwort or elodea
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Submerged plants absorb nitrates all day, every day
4. Tolerate a Little Algae & Duckweed
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Not all algae is bad—it feeds on nitrates
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Duckweed can shade the pond, reducing algae growth
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It’s not always pretty, but it can help balance your ecosystem
5. Careful Water Changes
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Only change 10–20% at a time
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Always dechlorinate tap water before adding it
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Test your tap water—if it contains nitrates, it could make things worse
What If You Still Have Nitrates?
Then it’s time to bring in the big guns.
We use and recommend Envii Nitrate Klear—our natural nitrate treatment. It’s packed with selected strains of beneficial bacteria that digest nitrates quickly and safely.
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Completely natural
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Safe for fish and wildlife
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Effective and fast
If you’re earlier in the nitrogen cycle (dealing with ammonia or nitrites), our product Filter Feed is a better fit. But once you’re in the nitrate stage—Nitrate Klear is your best bet.
Final Thoughts
Nitrates might be invisible, but their effects are not. If you want a clear, healthy pond—test often, plant smart, feed sparingly, and treat when needed.
Got questions or want to share your experience? Drop a comment or contact our support team—we’re always happy to help.
