Am I Overstocking My Aquarium? Clear Signs and Answers

Sometimes we compromise the space of our pet fish for our happiness. But I have so many fish keepers that are making the mistake of overstocking their aquarium without any information. Are you overstocking your aquarium, then? What are the things that can happen if you do so?

The general fish rule is to add one gallon for every additional inch of fish. However, you might make mistakes of not calculating fish to its full capacity growth. So, make sure that you know the maximum or average size of your fish and calculate the gallons in the same manner. Moreover, if your fish is small, you can compromise the rule while if your fish is big, you may need to add some extra gallons.

There is much more information regarding this topic which I will be covering through sub-sections for your ease. Make sure you go through all of it!

Reasons For Not Overstocking Your Aquarium

The way of overstocking aquarium is too mainstream but why is it not good for your aquarium? There can be many reasons for a fact. That is why being an aquarist is more of a choice rather than just a hobby.

Let us find out why you should not overstock your aquarium.


Overstocking leads to less oxygen in the tank. Fish are easily stressed due to the crowded environment and less space.

Not eating, gasping for air, different swimming patterns, loss of color, etc are the signs of stress you need to be alert about! Besides these, the fish may also hide, bully and face injuries.


When there is less space in the aquarium, the competition begins. In such a case, you might be ready to view bullying in the aquarium.

Either it is by groups to a single fish or by bigger fish to smaller fish, there occur quarrels. It can lead to fin nipping as well as poor health of the fish in your aquarium.


Fish can suffer from various diseases. These diseases are communicable too. That is why you might have seen that when one of your fish dies, most of them end up dead. Or the fish might also start showing irregular activities.

Fish require a lot of space. If they are not able to swim from here and there, they become anxious. Just imagine how you would feel to be locked in a congested room for the rest of your life with a lot of people! Doesn’t it make you sick? Yes, your fish feel the same way!

In case you find any kind of irregular activity or a sick fish, immediately quarantine the fish until it feels better.

Related articles:

Dangerous Water Parameters

When the number of fish in the tank increases, you must be ready for the amount of waste they produce. On top of that, stress makes the fishes eat less which adds up to the bio-waste.

Due to all these wastes, the nitrifying bacterias come into charge. A small amount of bacteria is good for the aquarium. But when the amount increases, the aquarium becomes full of nitrates and ammonia.

You can get the idea of how poisonous ammonia is in a fish tank and how to get rid of it from here.

This means there will be less oxygen in the tank and hence your fish will suffocate. So, if you see cloudy tank water, then it is probably because you are overstocking your aquarium.

Less Oxygen In The Tank

More fish in the tank means less oxygen for each fish. First of all, the amount of ammonia increases decreases the amount of oxygen in the tank. Similarly, the main source of oxygen in the water is the amount of water in the fish tank.

If you put in more fish, there will be less water in the tank. It means less oxygen per fish. Hence, your fish will gasp for air to filter the oxygen from the aquarium water through their gills.

Increase In Algae Growth In Aquarium

Algae in aquariums is a common problem. For those who are new to the aquarium world, algae grow where there is nitrogen compound. It can be both nitrate and ammonia.

Are there too many nutrients and too much light in your aquarium? Then, sadly the algae bloom can be uncontrollable.

So, the basic thing here is that if you have a high number of fish in the aquarium, you will contribute the food for algae to grow.

In contrast, a lesser number of fish means high oxygen and lesser nutrients for algae to grow.

You can thus try reading both my articles about algae control for more information:

Decrease In The Growth Of Fish

In simpler words, if you want your fish to be stressed, diseased, and have stunted growth, then an overcrowding tank is okay. You should understand here that it is cruel to place a big fish in a small tank.

The stress will decrease the immune system of your fish. Thus, causing it to grow at abnormal rates. Have you ever wanted to know why fish size estimates are larger in their natural habitat and less in aquariums? It is because of stress and overcrowding in the tank.

Dirty Water And Difficult Cleaning Process

If your aquarium water is too cloudy often and faces the problem of wastes being covered in the bottom of the tank, it is probably due to overcrowded tanks.

The bottom line is that aquarium filters are only able to filter the fish waste up to a maximum. Anything above that is difficult to process. The fish enthusiasts out there know how hectic it is to clean the tank and when it needs to be done often, it becomes even more irritating.

Every time I clean the tank, I have the process of having an anxiety spike beforehand. All thanks to issues of water quality! So, it is better if you do not overstock your aquarium!

Shorter Life Spans Of Fish

The saddest part of overstocking is that your pet will have a shorter life than usual. There is too much stress to handle with a weaker immune system in small aquariums.

Thus, your fish will suffer and suffocate. This is something that you do not want.

Am I Overstocking Fish In My Aquarium? Warning Signs!

Even when you are a beginner in fishkeeping, there are a few warning signs that you can figure out to know that you are overstocking your aquarium.

Some of the reasons not to fishkeeping are the warning signs themselves! However, if you are able to catch these signs, you will be more or less on the safe side.

The golden rule is also not applicable at many times, so some additional ways that you can know you are overstocking are:

Gasping Fish

When you are overstocking, your aquarium will lack enough oxygen for all fish. In such a case, your fish will come up to the surface for air.

Moreover, fish breathe through gills by converting water into oxygen. So, if you see your fish gasping for air or being stagnant than usual or even at the surface, then you should reduce the number of fish in the aquarium.

Cloudy Water

Like I explained earlier, too many fish create too many wastes. Similarly, the algae blooms and excreta can cause the aquarium water to become cloudy or even yellow in color.

If you see this happening frequently and find it difficult to clean your filter, then first you should clean the tank water. Next, you should decrease the number of fish in your tank.

Odd Behaviour Of Your Fish In Tank

If you are an experienced fishkeeper or even at an intermediate level, you will notice that every fish has its own behavior.

In a crowded room, the fish tends to change its behavior. You will notice inactivity in an active fish and an active/ aggressive nature among fish that are otherwise peaceful.

You will even see some fin nipping. There will be certain food preferences of your fish and fighting will occur while eating.

Another abnormal behavior is hiding a lot. This is due to excessive stress that the fish face as the existence comes to a crisis.

Furthermore, some might even stop eating or moving at all. If you think that all these activities are happening in your fish tank, immediately keep some fish in another tank.

Ammonia Spike

Fish produce ammonia. So the nitrogen cycle is always running when there is space. However, when the number of fish is high, ammonia spikes.

For this, you must check the quality of your water from time to time through the water test kit. You can use the absolute best, API FRESHWATER MASTER TEST KIT 800-Test Freshwater Aquarium Water Master Test Kit, White, Single.

To decrease the spikes in ammonia, you can try water changes, cleaning the fish tank, and even using some water de-chlorinators.

Tips On How To Avoid Overstocking Fish In Your Aquarium

Now that you know that overstocking your aquarium is harmful and has many disadvantages, you should learn how you can avoid doing so. The first and foremost thing is to learn about the warning signs but they are to be done after you have overstocked your aquarium already.

If you ask me, it is better not to overstock the aquarium in the first place and save yourself some time and effort. This will also make you the best owner of your pet fish as they will be more than happy with you.

Start With Few Numbers

So, it is best to start with fewer numbers and gradually add up if there is space. Remember that space does not just mean a free area to live. It also means an area to be free and swim across for fishes.

By learning to start with a few, you will be able to learn the behavior of the fish as well as prepare yourself for what is coming next. I would definitely suggest you start with easy small fishes so that they can get the aquarium cycle ready for the others.

Great species to start with are guppies, neon tetras, and goldfishes. These species are more hardy than other species in the fishkeeping world.

Leave Space For Growth Up To Full Potential

Many beginners make the common mistake of underestimating the growth of their fish. They bring in small-sized fish and forget that they will grow later. Hence, keep on stocking the aquarium until it looks absolutely the perfectly stocked aquarium. However, in a few weeks, the same aquarium will be overstocked.

This is why I have mentioned two different rules so that you can estimate how many gallons you have to separate for a fish each.

Just remember that the fish will grow again. You cannot fit in a grown-up in a wardrobe he used to fit when he was a baby. It is the same with fishes too.

Consider Some Gallons For Fries

You have to understand that the fish will reproduce at least once in their lifetime. If you keep just the maximum amount of fish in the aquarium, you will never be able to see the fries.

Many fishes eat their own babies. What’s more? If they do not, other fish in the aquarium will. So, the thing that you can do is leave some gallons for fries.

In that way, at least they have a chance to survive as there is space to remain hidden. Moreover, you just need some spare time to keep them alive until you separate them into a fry tank.

If you are looking for breeding, check out how you can make a profit by learning about the easiest fish to breed in a home aquarium.

Learn About The Fish You Are Going To Pet

The basic thing to learn when you are setting aquariums is to learn what parameters your fish lives in. Every fish is comfortable with a type of aquarium setting. So, you have to set the aquarium in the same way to lengthen their life.

If your fish poops more, you need to keep less fish in the aquarium even though there is space. Since the excreta will increase the number of nitrifying bacterias and get the cycle going, it can get toxic if you add more to the tank.

So, how do you know about such things? A great way to know about this is by checking in the pet store beforehand. Just observe for the first few days or even for a day and then decide on your own. Or you can even use the first point of adding little by little.

Similarly, you might need to add a school for some fish like guppies, neon tetras, etc. while keeping some fish alone like angelfish. Also, consider such things.

Standard Rule

If all of this seems a lot to follow, you can just go with the standard rule too. The rule is:

For Small Fish

RULE: 1 gallon of water for 1 inch of fish or 10 liters of water for 3 grams of fish

Small fish include fish like guppies, neon tetras, ember tetras, rainbowfish, bettas, etc.

For large fish

RULE: 3 gallons of fish for 1 inch of fish

Large fish include Catfish, Oscar fish, Koi fish, etc. Since they cover the larger surface area, they need more water per inch of fish.

Remember that these rules are just guidelines, you have to consider the above matters like the fish species in order to get the accurate result. However, this rule can keep you on the safe side too!

What To Do To Avoid Overstocked Aquarium Disadvantages?

The first thing to do is not to overstock your aquarium. It is a common thing to know and understand. However, what else can you do?

If you really want to add just a few more fish than the optimum amount. Add a wet/dry filter. It adds some gallons to your tank. Thus, creating space for your fish. In addition, it also adds up the oxygen in the tank with the trickle method without changing the current. The best of all.

But it will also not be able to take more than what it capacitates. So, make sure you do not overutilize the aquarium filter!

Will Adding Aquarium Filter Provide Help In Overstocking?

Well, the simple answer to this is no. The capacity of the filter does not add up to clean the tank full of waste. It is even harder to get the toxins out. They just collect the waste and reduce toxicity. Hence, when the amount increases, it becomes harmful.

It is better not to overstock the tank in the first place but filters like wet/dry filters will help you to add some extra gallons in the refugium. However, do not depend too much on it too!

Frequently Asked Questions

How Do I Know If My Aquarium Is Getting Enough Oxygen?

Have you seen your fish over the surface recently? This might be a sign that your aquarium lacks sufficient oxygen. It is a similar case if they are roaming around your filter output.

These areas in the aquarium have high oxygen levels as the disturbed surface creates space for oxygen.

How Can You Tell If An Aquarium Is Safe?

An aquarium is the safest equipment and a long-term investment. The glass equipment lasts about a hundred years.

So, all you need is the aquarium decorations to be safe too. In such a case, you can use pottery like plates, bowls, and mugs. These potteries must be dishwater-safe to be fully aquarium safe.

Can You Put Too Much Oxygen In A Fish Tank?

Nothing is good when it is too much. Adding too much oxygen can cause diseases in your fish. The aquarists call it lethal gas bubble disease.

This disease causes the gas to come out from the fish. Moreover, the disease can create bubbles in the skin. Adding to it, your fish will also suffer from bubbles around the eyes.

It can be a painful experience for both you and your pet fish.

Last Words

In a nutshell, you have to take care of a lot of things to make sure that you do not overstock your aquarium. Being an owner of an aquarium is being aware of what makes your pet fish happy and healthy.

Hence, make sure that you learn about the size, nature, and water parameters that your fish lives in so that you can create a better place for the fish. You can even use the standard golden rule to be on the safe side!

Make sure to share your experiences in the comment section below! Also, add up points if I have missed any.