Why is It Necessary to Wait 24 Hours to Put Fish in The Tank?

If you are just entering the world of fishkeeping, you may have heard that you should wait a certain amount of time before putting a fish in a tank.

Most people will tell you that the rule of thumb is that you need to wait for at least 24 hours before you put a fish directly into a tank.

So, why do you need to wait this long to put your fish in the tank? There are a few different reasons.

A Note on Taking Your Fish Home

When you buy a fish, you get the little critter inside a water-filled plastic bag. Fish are easily stressed out, and this can happen for a litany of reasons.

When it comes to transporting and adding a fish to a new tank, the very act of moving it can cause stress, as can a temperature change and changes in scenery, pH levels, tank mates, bacteria levels, and more.

Let’s look at all of the reasons why you need to wait for at least 24 hours to put your fish into the tank.

Moving Stress

You want to wait for 24 hours to put a fish in a tank due to transportation stress. Fish don’t like changes in scenery, and moving too far causes stress, even death.

When you first get home, instead of putting the fish directly into the tank, you first want to put the whole bag in the tank.

Just hang it off the side, and then eventually, you can open up the bag to let the fish out.

You should avoid moving the fish too many times in a short period—from the store to a bag and then to a new tank.

Moreover, introducing your fish to new fish right after being taken out of an old tank can be stressful. Therefore, putting the whole bag in the new tank will allow the fish to adjust to its new surroundings without being overwhelmed.

Temperature and pH

We are still talking about putting the whole bag in the water and allowing it to sit there for up to 24 hours.

Another reason for this is due to water temperature and pH levels. Fish are very sensitive, and each type requires a specific pH level and temperature.

Moreover, although fish can often handle varying levels of both, fast changes are not good. Fast temperature or pH changes can lead to severe problems.

Therefore, you want to put that bag of water, with the fish, inside the tank so that the water inside the bag can slowly change to the same temperature as the water within the tank.

Next, you want to poke a little hole in the bag after the first few hours, which will allow the water in the bag to mix with the water in the tank. This will allow for a gradual change in pH, so it’s not too fast.

After the water has been mixed and the water in the bag and the aquarium are the same temperatures, can you let the fish out into the tank.

The Nitrogen Cycle

Perhaps the most crucial reason you want to wait for at least 24 hours before putting a fish in a tank, particularly a new tank, is the nitrogen cycle.

Each fish tank needs to be cycled before fish can go into it. You see, all aquariums have bacteria, beneficial bacteria that break down poisonous ammonia and nitrates.

Without these bacteria, ammonia and other such substances build up in the tank, and even the smallest amount of ammonia can kill fish.

Simply put, you should allow some time for the biological filter media and the rest of the tank to build up a healthy bacteria population.

Now, this can take anywhere from 3 to 5 weeks. However, if you get some water conditioner and a unique nitrogen cycle booster, you may be able to reduce this time to just 24 hours.

Whatever the case, remember that putting fish into a tank that has not yet cycled is dangerous and often results in the death of the fish put into that tank.


The bottom line is that you never want to fill a tank with water and immediately plop a fish into it.

You also don’t want to put a fish that you just bought directly into a tank as soon as you get home. Setting up an aquarium that is healthy for the fish takes time.