is supported by our readers. When you buy through links on our site, we may earn a commission. Learn more.

Why Did My Fish Die? (Four Common Beginner Mistakes)

So…you set up your aquarium and finally got some fish. Within a few hours/days, your new friends were no more. While this can be tough, it is actually much more common than you would think.

As with many things in life, setting up a fish tank takes time. Rushing the process can lead to many mistakes, which reflect poorly of the health of your fish.

If your fish died shortly after placing them in your tank, you most likely made one of the mistakes below. In this article, we will discuss the most common mistakes and how you can fix them!

Why Did My Fish Die?

If your new fish died quickly after being introduced to your tank, it was most likely caused by one of these issues:

1. You Didn’t De-Chlorinate the Water

Water from the tap is safe to use, but only after it has been treated.

Tap water contains small traces of chlorine. This chlorine is safe for human consumption, but is very toxic to fish. If your fish died within a few hours of being placed in the tank, this is the reason.

No matter how small of an amount of water you are adding to your tank, make sure you always treat it with water conditioner. I recommend API Tap Water Conditioner.

2. New Tank Syndrome

This is by far the most common mistake made by new fish keepers.

Most people think that setting up a fish tank is as easy as filling a tank and throwing some fish in there. Unfortunately, this is not the case. Before you can add fish to a new aquarium, you must cycle the tank.

When fish produce waste, it breaks down into Ammonia. This is extremely toxic to fish and will kill them within a few days. To combat this, you must allow beneficial bacteria to grow, which helps convert the Ammonia to non-toxic substances.

If you want to learn more about this process, you can check out our complete cycle guide.

3. Sudden Changes in Temperate or pH

Fish are delicate. Between getting shipped to the pet store, bagged up, and brought to a new home, odds are against them from the beginning. Many people will get home and just dump their fish straight into the tank. This is a big mistake.

When bringing your fish home, make sure you don’t expose it to any sudden changes. This includes temperature and pH. You should always acclimate your new fish to your tank water before dumping it straight in.

One way to acclimate your new fish to temperature differences is by floating the bag in the tank. This slowly bring the water in the bag to match the temperature in the tank, reducing the risk of shock. I would recommend floating it for at least 30 minutes or so.

During this time, you should also be slowly adding a little tank water to to the bag every few minutes. This acclimates the fish to the new pH and element levels of your tank.

4. Sickness/Disease

If you brought your fish home and it dies within a few days, there is a possibility it was sick when you bought it. Unfortunately, this is a very common problem since conditions at chain pet stores are usually awful.

When looking for a new fish, make sure everything in the tank is swimming strong and normal. Any erratic movements, torn fins, or discolorations can indicate future problems.

One of the best things you can do is ask an employee to feed the tank. Watch the fish you are looking to purchase. If it eats normally, chances are good that it’s healthy. Sick fish almost never eat.

In addition, check all of its fins carefully. Make sure it doesn’t exhibit any signs of fin rot (a potentially fatal disease for most fish). If all of this looks good, take your new fish home!

Closing Thoughts

Fish are delicate creatures. While there are many unavoidable problems when it comes to fish, there are also many avoidable ones.

If you brought your new fish home, only to find it dead within a few hours/days, you probably fell victim to one of these mistakes. Don’t feel bad, though; it happens to most people in the beginning.

By being aware of common mistakes and knowing how to avoid them, you new fish should live love and happy lives. Check out our guide on “How To Set Up Your First Fish Tank” if you would like some more info on the subject.

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

Leave a Comment