Fast & Natural Fixes + Long-Term Prevention
Ammonia is a silent killer in new and established aquariums. Even low amounts of ammonia can burn fish gills, cause lethargy, and lead to sudden death for fish. This is especially true for beginners during the first few weeks of cycling. I’ve been there. My first tank hit a spike, fish were gasping, and the water smelled awful. After freaking out a little bit, I got it fixed with some quick methods I found online, and then learned how to keep it from happening again. So, let’s jump right into how to lower ammonia in a fish tank!
In this guide, I’m going to cover:
- Why ammonia spikes happen
- Fast emergency fixes to drop ammonia quickly (hours to days)
- Natural long-term solutions to keep it at zero safely
- Best products that actually work
- Step-by-step prevention so it never returns
Affiliate Disclosure: Some links earn us a small commission at no extra cost to you — helps keep these guides free! Let’s save your fish and get your tank stable!
What Causes High Ammonia in Your Fish Tank?
Ammonia (NH3/NH4+) comes from several main sources. Fish waste, uneaten food, decaying plants, and any other dead critters in the tank all add to the problem. In a healthy tank, beneficial bacteria turn it into nitrite, and the nitrogen cycle begins. But if the cycle isn’t established or gets disrupted, ammonia spikes fast.
Most common causes:
- New tank syndrome (no bacteria yet) — classic for beginners. See my post on the Best Starter Bacteria
- Overfeeding — uneaten food rots quickly.
- Dead fish/snails/plants — hidden decay releases huge amounts of ammonia.
- Overstocking — too many fish in your tank for the bacteria to handle.
- Cycle crash — from fish medication to big water changes, and cleaning the filter with tap water.
- Poor filtration — a weak or clogged filter can’t process waste.
Ammonia Symptoms In Fish: Fish may be gasping at the surface, red/purple gills, be lethargic, have clamped fins, and experience sudden death.
Fish Tanks may smell like urine/ammonia. I recommend that you test your tank’s water immediately. Anything above 0.10 ppm is dangerous; 0.50+ is an emergency!
Emergency Fixes: How to Reduce Ammonia Fast in a Fish Tank (Hours to 2 Days)
When ammonia is high, act fast; every hour counts.
Large Water Change (30–50%)
Remove 30–50% of the water immediately and replace it with dechlorinated, temperature-matched water. Here’s a link to my guide on the best pump for aquarium water changes.
Use a siphon/pump to vacuum debris and uneaten food.
Repeat 25–30% daily until ammonia is below 0.10 ppm
Why this works: You are directly diluting the ammonia-filled water. This method removes ammonia instantly.
Add a Strong Dechlorinator/Ammonia Neutralizer
Use something like Seachem Prime or API Stress Coat. These will detoxify ammonia and nitrites. These will work for around 24–48 hours, giving time for the bacteria in your tank to catch up.
Dose per instructions on the bottle. In my opnion, Seachem Prime is stronger for emergencies.
Pro tip: Double dose on first use if levels are very high.
Boost Beneficial Bacteria
Add bottled bacteria like FritzZyme or Tetra SafeStart. They both help rebuild the bacterial cycle fast.
Run 24/7 with an air stone for oxygen for an oxygen boost.
Increase Oxygenation
Add an air stone or bubbler if you aren’t already using one. More oxygen that is pumped in helps fish survive and speeds up bacterial growth in the tank.
See my guide to the best fish tank air pump guide for quiet options if you need an air pump.
Remove the Source
Scoop any dead fish, snails, or rotting plants ASAP.
Stop feeding for 2–3 days. You may feel bad for the little ones in your tank, but fish are tough, and they can survive a couple of days.
Your short-term goal: Get ammonia to below 0.10 ppm within 24–72 hours. Retest every 12 to 24 hours.
Case Study: The “Hidden” Ammonia Spike in My 50-Gallon Tank
A few years ago, I noticed my Harlequin Rasboras were hovering near the surface and their gills looked slightly inflamed. I did a quick test and was shocked to see my ammonia at 0.50 ppm—in a tank that had been stable for two years!
The Investigation: I didn’t see any dead fish, but after moving some driftwood, I found a snail that had passed away behind the filter intake. In a smaller tank, that much decaying organic matter would have been a total disaster.
My Recovery Plan:
- With in about 30 minutes, I performed a 50% water change and used a double dose of Seachem Prime to protect the fish from the remaining 0.25 ppm.
- A capful of Seachem Stability was added directly into the filter media to help the bacteria colony recover from the sudden waste load.
- I stopped feeding for 48 hours. By day three, the levels were back to a perfect 0.
The Lesson: Even a “perfect” tank can spike. Now, I do a regular “headcount” of my snails and larger fish during morning feeding.
Best Products to Lower Ammonia Quickly and/or Naturally
Here are some great products that have really helped me out along the way.
Seachem Prime
About: It is great at detoxifying ammonia, nitrites, and heavy metals.
How I Use It: I don’t just use Prime for water changes. During an ammonia spike, I dose for the entire volume of the tank, not just in the new water. I also keep a small 5ml syringe in my aquarium cabinet specifically for Prime. It’s much more accurate than the ‘thread-count’ method on the cap, especially for my smaller nano tank.
Cost: Starting at about $4.00 and going up to $70, depending on size
Where to get it: Amazon.com
Reviews:4.8/5 Stars (41,441 reviews)
Seachem Stability
About: It helps to facilitate the breakdown of waste organics, like ammonia, nitrite, and nitrate.
How I Use It: Whenever I’m dealing with an ammonia spike, I pour my dose of Stability directly into the filter intake or onto the sponge media rather than just dumping it in the water. I want those ‘good’ bacteria to hit the filter pads immediately, where they can start colonizing and eating ammonia right away.
Cost: About $18
Where to get it: Amazon.com
Reviews: 4.8/5 Stars (12,955 reviews)
FritzZyme 7
About: This is a nitrifying bacterium, proven to quickly reduce toxic ammonia and nitrite levels.
How I Use It: Because this contains live bacteria cultures, I always check the expiration date on the bottle before buying. When I use it, I turn off my UV Sterilizers for at least 48 hours. If you leave a UV light on, it can kill the beneficial bacteria before they have a chance to settle into your substrate and media. This stuff stinks. Keep the lid on tight.
Cost: About $20
Where to get it: Amazon.com
Reviews: 4.6/5 Stars (3,336 reviews)
API Quick Start
About: Lowers ammonia or nitrites.
How I Use It: I find Quick Start is most effective when I’m adding new fish to a stable tank. I’ll add a dose about 10 minutes before I release the new arrivals. It provides a quick ‘safety net’ for the biological filter as it adjusts to the increased waste load from the new inhabitants.
Cost: About $18
Reviews: 4.8/5 Stars (9,776 reviews)
Hornwort
About: It acts as a natural filter for your tank.
How I Use It: I call this my ‘Ammonia Sponge.’ In an emergency, I don’t even bother planting it in the substrate. I just let it float at the surface, where it’s closer to the light. This allows the plant to grow faster and absorb ammonia through its needles at an incredible rate.
Cost: Around $10-$20
Where to get it: I recommend getting live plants at a garden center or a reputable aquarium store.
Duckweed
About: It acts as a natural filter for your tank’s water.
How I Use It: The same way as the Hornwart. The only difference is that I never have to actually plant it. The Duckweed just hangs out on top of the water.
Cost: Under $15
Where to get it: I recommend getting live plants at a garden center or a reputable aquarium store.
Natural Long-Term Solutions For How to Keep Ammonia Low In Your Fish Tank
Once the emergency is over, focus on natural, sustainable methods. The following solutions and habits have helped me so much with my fishkeeping. Please do yourself a favor and at least try them out. You won’t regret it!
- Add Live Plants (Best Natural Filter)
- Use Fast growers like hornwort, duckweed, water sprite, and java moss absorb ammonia directly
- Add 5–10 stems or a handful of floaters. These can cut ammonia in weeks.
- I have a post on easy fish tank plants that is great for beginner picks.
- Strong Biological Filtration
- Use sponge filters, ceramic rings, or bio-media. This gives bacteria tons of surface area to grow.
- Proper Feeding & Stocking
- Feed only what fish eat in 2 minutes, 1–2 times/day.
- Follow the 1-inch-per-gallon rule. This way, your fish won’t be crowded.
- Weekly Water Changes
- 20–30% weekly, with a pumpthat dilutes ammonia before the spikes happen.
- Cycle Your Tank Properly
- Never add fish all at once. Try a fishless cycling or add fish to the tank slowly.
- Test Tank Water Weekly
- This is the best way to avoid not only ammonia, but a whole bunch of other water-related problems with your tank. I have a post on the best Test Kits for Aquariums you may want to see if you aren’t sure about what you need to test.
- Quarantine New Fish
- Keeping new fish separated for a short time can do a lot to prevent disease and start a spike in ammonia levels.
Frequently Asked Questions (FAQs)
How fast can I lower ammonia?
With 30–50% water changes, Prime and bottled bacteria, you can drop ammonia from dangerous levels to close to zero in around 24–72 hours. Daily 25% changes + bacteria booster is the fastest combo. Keep testing every 12 hours during the emergency.
What’s the fastest ammonia remover?
Seachem Prime is the fastest. It detoxifies ammonia instantly (makes it non-toxic for about 24–48 hours) while you do water changes and add bacteria. It’s the go-to emergency product for beginners and pros.
Are natural methods enough for a spike?
Natural methods (plants, water changes, better filtration) are best for long-term control and prevention, but during a severe spike, they’re too slow alone. Combine them with Prime or Stability for quick relief, then rely on plants and routine for maintenance.
Can plants remove ammonia?
Yes! Fast-growing plants like hornwort, duckweed, and water sprite absorb ammonia directly as fertilizer, often dropping levels by 10–20 ppm per week in stocked tanks. They’re the best natural long-term solution. Try adding them after the emergency is over.
Is it safe for fish during these fixes?
Yes, if you avoid full water changes (30–50% max per day) and use Prime to detoxify ammonia. Watch for stress (gasping, hiding). Add an air stone for an oxygen boost and go slow to keep fish safe.
How to test for ammonia in my fish tank?
Use a digital tester, liquid kit, or even test strips. Dip the probe or strip/ add drops to a sample, wait, and compare. Digital is the fastest, and liquid test kits are the most accurate (see my digital tester post and my best testing kit post). Test daily during spikes, then weekly for maintenance.
Ammonia vs nitrite — which is worse?
Nitrite is more immediately toxic (even 0.5 ppm can kill), but ammonia is the first spike in a cycle crash and must be fixed first. Both are deadly. Aim for zero of each. Use Prime to detoxify both during emergencies.
Can over-cleaning cause ammonia spikes?
Yes! Cleaning filter media in tap water kills beneficial bacteria, causing ammonia to spike. Always rinse in old tank water only, and never clean everything at once. Try doing 1/3 of media per month.
Best product for an emergency ammonia spike?
Seachem Prime. It detoxifies ammonia/nitrite instantly, is safe for fish, and works in freshwater/saltwater. Double dose in severe spikes for 24–48 hours of protection while you do water changes.
Is there a way to prevent ammonia spikes forever?
Feed lightly (2-minute rule), stock conservatively (1 inch/gallon max), change 20–30% weekly, add plants, maintain strong filtration, and test regularly. A mature cycle + these habits = zero spikes.
Conclusion
Ammonia spikes are scary, but you now have the tools to handle them fast and prevent them forever. For emergencies, do big water changes + Seachem Prime + bottled bacteria to drop ammonia quickly. For long-term stability, add plants, feed sparingly, and keep up weekly maintenance.
Comment on your current ammonia reading and tank size. I’ll give you a custom plan if you need a little help. You’ve got this! Clear water and happy fish are just a few steps away!
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