How to Reduce Ammonia in a Fish Tank

Ever noticed your fish acting a little “off”? Or caught a whiff of that telltale smell when you walk by the tank? That might be ammonia. But don’t worry — you’re not powerless against it. It’s totally manageable if you know what you’re dealing with.

In this guide, we’ll break down everything you need to know how to reduce ammonia in a fish tank. Let’s dive in!

What Is Ammonia and Why Should You Care?

Ammonia is basically toxic waste for your fish. It’s a natural byproduct of your tank’s ecosystem, mostly coming from fish waste, uneaten food, and other organic material breaking down. While it’s a normal part of life in an aquarium, it’s also highly toxic to fish.

Now, your fish can’t exactly tell you, “Hey, I’m swimming in poison here!” Instead, they’ll show signs like stress and struggling to breathe. Left unchecked, ammonia can turn your tank from a cozy home into a danger zone.

And it’s sneaky — ammonia doesn’t have a color, so you won’t spot it just by looking at the water. That’s why it’s so important to understand what it is and how to manage it.

How to Spot High Ammonia Levels in Your Tank

Ammonia can lurk beneath the surface. Thankfully, your fish and water can give you clear warning signs — if you know what to watch for.

1. Your Fish Are Acting Weird

Fish are great at letting you know something’s off — just not with words. Here’s what to look for to see if they’re experiencing ammonia poisoning:

• Gasping at the surface (like they’re out of breath).
• Lethargy or unusual sluggishness.
• Clamped fins (their “I’m stressed” pose).
• Red streaks or irritation on their gills or body.

2. Your Water Looks or Smells Funny

Although ammonia is colorless, cloudy water in your fish tank can signal that organic waste is building up and converting into ammonia. Also, a bad smell — think “swampy” or “rotten” — is a strong clue that ammonia levels are high.

3. Testing, Testing… Testing!

Don’t just guess — grab an ammonia test kit to be sure. Ammonia is sneaky, and the best way to catch it is with an aquarium test kit. These kits give you a quick reading, and ideally, you want the result to be 0 ppm (parts per million). Anything higher? Time to take action.

What Causes Ammonia to Spike?

If ammonia is causing chaos in your tank, it didn’t just appear out of nowhere. Something tipped the balance, and understanding the culprits will help you fix the issue — and prevent it in the future.

• Overfeeding: “Just one more pinch” might feel like love, but uneaten food quickly breaks down into ammonia. If it’s sinking to the bottom and staying there, it’s a problem. 
• Overstocking: Too many fish, not enough space. More fish means more waste, and if your tank isn’t big enough to handle it, ammonia levels skyrocket.
• Insufficient filtration: If your filter’s too small, clogged, or not maintained, it can’t keep up with the waste. Hello ammonia spike! 
• Skipping maintenance: Neglecting water changes or gravel cleaning allows waste and debris to pile up — and guess what that turns into? Yep, ammonia.
• New tank syndrome: Setting up a new tank? Without enough beneficial bacteria, your tank can’t break down ammonia properly. This is a common issue in uncycled tanks, called new tank syndrome.
• Decaying organic matter: Dead plants, uneaten food, or even a sneaky dead fish hidden in the tank can all contribute to rising ammonia levels.

How to Reduce Ammonia in a Fish Tank — Quick Fixes

Uh-oh, your ammonia levels are up, and your fish are feeling the heat. Don’t panic — here’s what you can do right now: 

1. Change the water: Not too much! Swap out 25-30% of the water with fresh, dechlorinated water. This dilutes the ammonia without shocking your fish. 
2. Clean the tank: Get all that decaying organic matter out to stop ammonia from building further. Siphon like a boss with our step-by-step guide!
3. Rinse the filter: If your filter is clogged, it’s not doing its job. Be gentle! Give it a rinse using tank water — not tap water — to preserve the good bacteria while clearing out gunk.
4. Use an ammonia detoxifier: Grab a water conditioner that neutralizes ammonia. It’s a lifesaver in emergencies and keeps your fish safe while you work on the root cause. We recommend Seachem Prime or Seachem Safe for freshwater tanks. 
5. Test, test, test: Keep an eye on ammonia levels daily with your test kit. Did you know you don’t need to take out an entire test kit just to test ammonia levels? We love using Seachem’s Ammonia Alert to have a quick view! 

Long-Term Ways to Keep Ammonia in Check

Once you’ve tackled the immediate ammonia crisis, it’s time to think long-term. These strategies will help you keep your tank healthy and ammonia-free for the long haul.

1. Cycle Your Tank Properly

Before adding fish, make sure your tank is fully cycled. Cycling builds up beneficial bacteria that break down ammonia into less harmful substances. If you’re not sure how, don’t worry — we have a beginner-friendly guide.

2. Feed Smart

Stick to feeding your fish what they can eat in 2-3 minutes, twice a day. If food’s left floating or sinking, it’s too much. Less waste = less ammonia. Learn more about proper fish feeding habits. 

3. Keep Up With Water Changes

Routine water changes — about 20-25% weekly — are the easiest way to maintain water quality. Fresh water means less ammonia buildup. 

Did you know there’s more to keeping your tank clean than water changes? You’ll need to follow a fish tank cleaning routine to keep ammonia (and other things like algae) at bay!

4. Choose the Right Filter

Invest in a good-quality filter that’s the right size for your tank. Bonus points for one with biological media to encourage beneficial bacteria growth. 

We’ve reviewed some of the best filters on the market if you want to check it out. 

5. Don’t Overstock Your Tank

Research how much space your fish need and avoid overcrowding. More fish = more waste = more ammonia. Keep it balanced.

Here’s how you can choose the right tank size for you and your fish!

6. Add Live Plants

Live plants do double duty — they look great and absorb ammonia as part of their natural growth process. Think of them as your tank’s green cleaning crew.

Not sure whether you’re ready for live plants? We got you!

7. Monitor Regularly

Test your water weekly to keep tabs on your water’s chemistry — from pH, GH, and KH to ammonia, nitrites, and nitrates. Catching small changes early prevents big problems later.

8. Quarantine New Additions

Before adding new fish, quarantine them in a separate tank for a couple of weeks. It helps prevent stress and reduces the risk of introducing extra waste or disease.

Join the KaveMan Aquatics Family!

Dealing with ammonia might feel overwhelming at first, but with the right steps, you can tackle it and keep your fish happy and healthy. It’s all part of the journey of being an awesome fish keeper! But you don’t have to go through this journey alone! Join the KaveMan Aquatics Family and get access to everything you need to thrive as a fish keeper!

• In our Facebook group, you’ll be surrounded by friendly fish keepers who are always ready to help and share their experiences.
• Over on Discord, you’ll get exclusive content, access to live Q&A sessions, and a chance to connect with fellow enthusiasts around the world.
• Plus, on YouTube, you can watch behind-the-scenes content, participate in live streams, and ask me anything — it’s all about helping you grow as an aquarist!