What Causes Ammonia to Build Up in a Fish Tank? And How to Stop It Before It Wrecks Your Tank

Table of Contents

• What is Ammonia Anyway?
• Why Does Ammonia Build Up in Fish Tanks?
• How to Stop Ammonia From Becoming a Problem
• What to Do When Ammonia Spikes
• The Bottom Line

Alright, so here we are. If you are dealing with a fish tank, or thinking about starting one, ammonia is one of those words you will bump into sooner or later. Trust me, it is not your friend. Think of it like that relative who shows up at family gatherings, causes ammonia chaos, and leaves everyone stressed out. It just does not belong.

Now, for anyone new to keeping fish or shrimp, ammonia is this sneaky chemical that builds up in your tank if you are not careful. And when it does, it hits hard. It is toxic, it burns fish gills, and if you let it go too long, it can lead to fish floating belly-up. Nobody wants that. I sure do not.

But let us take a step back and figure out why ammonia builds up in the first place. What is causing it? And more importantly, how do we prevent it from happening in the first place? It is not rocket science, but you do need to know the basics.

What is Ammonia Anyway?

Ammonia comes from waste. Yep, plain old waste. It shows up in your tank because of fish poop, leftover food, dead plants, and any other organic stuff that breaks down in the water. When you have fish, shrimp, snails, or even plants, they are all adding to the mix. As things decay, ammonia gets released into the water.

In a perfect world—or at least a well-maintained tank—your bacteria step in and handle that ammonia like pros. They break it down into less harmful stuff through something called the nitrogen cycle. The ammonia gets turned into nitrites, and then into nitrates, which are much safer for your fish. The trick is keeping that balance so the bacteria can do their job before the ammonia gets out of hand.

The trouble comes when you have too much waste, too many fish, or not enough bacteria to handle the load. Then the ammonia starts to pile up, and you can bet your fish will let you know something is wrong.

Why Does Ammonia Build Up in Fish Tanks?

Now that we know what ammonia is, let us talk about what actually causes it to spike. I see people make the same mistakes over and over again, especially when they are just starting out. And look, I made these mistakes too when I got started. It happens. But once you know what to watch for, you can keep that ammonia in check without too much hassle.

1. Overfeeding: The Classic Rookie Move

Let us be honest, we have all been there. You get excited about feeding your fish, and before you know it, you have dumped in way more food than they can possibly eat. Maybe you think they are hungry. Maybe they just look cute. Either way, you toss in that extra pinch, and they nibble at it for a few minutes before swimming off. The rest? It sinks to the bottom, rots, and starts cranking out ammonia like nobody’s business.

How to avoid this?

• Feed your fish a little less than you think they need. Watch them eat. If there is food left after a couple of minutes, scoop it out. No need to let it sit there and stink up the tank.
• Try an automatic fish feeder. It is a great way to keep things on track, especially if you tend to forget when you fed them.

2. Too Many Fish, Not Enough Space

The more fish you have, the more poop you get. It is pretty simple. Too many fish in a small tank means your waste production is going to skyrocket. And when that happens, your filter and bacteria are going to have a hard time keeping up. Ammonia levels rise, and before long, you are in trouble.

What can you do?

• Stick to that old one-inch-of-fish-per-gallon rule as a guide. It is not perfect, but it will help you avoid overcrowding.
• If you have got a lot of fish and you start noticing the water getting cloudy or your fish acting stressed, it might be time to get a bigger tank or add more filtration.

3. Incomplete Nitrogen Cycle

Here is where things get a little technical, but bear with me. If your tank is brand new, it has not had time to build up enough bacteria to handle the ammonia. Without those bacteria, the ammonia just sits there, making your fish miserable. This is called an incomplete nitrogen cycle, and it happens a lot when people rush to set up their tanks.

How to fix it:

• Cycle your tank before adding any fish. This means letting it run for a few weeks with just water and a small ammonia source, like fish food, to help the bacteria grow. Learn more about the nitrogen cycle in our guide on understanding the nitrogen cycle.
• Use a bacterial supplement to jump-start things. API Quick Start is a good one to get things going faster.
• Keep an eye on your ammonia levels with a test kit, and only add fish when those numbers are stable.

4. Dead Fish or Plants

Here is one people sometimes forget. Dead fish or plants left in the tank will start to decompose, and when they do, they release ammonia into the water. It is not pretty, and it can sneak up on you if you are not paying attention. I have had a snail or two disappear in the past, only to find them weeks later tucked behind some plants. The ammonia spike from that little critter decomposing can really mess things up.

To stay ahead of it:

• Do a headcount regularly. If anyone is missing, check the nooks and crannies of your tank.
• Remove any dead plants or fish as soon as you spot them. Do not let them rot in there.

How to Stop Ammonia From Becoming a Problem

You have learned why ammonia shows up in your tank, so let us talk about what you can do to keep it under control. Keeping ammonia levels down is about staying on top of your tank’s maintenance and watching for any early signs of trouble.

1. Feed Sparingly

This might be the easiest change you can make. Feed your fish only what they will eat in two to three minutes. If there is food floating around after that, you are overfeeding. Less food means less waste, which means less ammonia.

2. Clean the Tank Regularly

Look, I know cleaning the tank is a chore, but it is one of the best things you can do to keep ammonia in check. Do a 25-30% water change every week or two, and vacuum the gravel to get rid of any hidden waste. If you notice the water getting cloudy or the fish seem stressed, bump up the cleaning. For more tips, check out our article on how to maintain a clean aquarium.

3. Get a Good Filter

You need a filter that can handle the waste in your tank. That means something with good biological filtration that can help break down ammonia. Pick a filter that is rated for your tank size, and if you have got a lot of fish, get something a little bigger just to be safe. Learn more about filters in our post on choosing the best aquarium filter.

4. Test the Water

Invest in an ammonia test kit. These things are lifesavers. Regular testing helps you catch any spikes before they get out of control. You do not need to be obsessive, but checking your water every week or so can save you from a big headache down the road.

What to Do When Ammonia Spikes

Let us say you have tested your water and found that ammonia levels are creeping up. Here is what you do:

Do a Water Change:

Swap out about 30-50% of the water right away. This will dilute the ammonia and give your fish some immediate relief.

Use Ammonia Neutralizers:

Products like Seachem Prime are a quick fix. They will neutralize the ammonia for a short time, giving you a chance to figure out what is causing the spike.

Check for Dead Stuff:

Look for anything dead or decaying in the tank. This includes plants, fish, and even snails. Remove anything that could be adding to the ammonia problem.

Upgrade Your Filter:

If your filter is not doing the job, it is time to upgrade. Add a secondary filter or get one that has better biological filtration to keep ammonia levels in check.

The Bottom Line

Ammonia is no joke, but with a little attention to detail and some regular maintenance, you can keep your tank running smoothly. Feed your fish wisely, clean up regularly, and keep an eye on your water quality. That way, you can avoid the stress of an ammonia spike and keep your fish happy and healthy.

If you need gear, whether it is ammonia test kits, filters, or water conditioners, check out the stuff we have got in our shop. I have personally tested everything, and I would not recommend it if I did not think it was solid.