How Long Do You Have to Wait to Put Fish In a New Tank

Most people, myself included, normally put fish in a new tank right away. Following the “set the bag in the tank so that the water gets to the correct temperature, and then slowly add your fish” directions. This could be part of the reason that 95% of my fish didn’t make it more than a week. The other 5% was fish that were won at the state fair, and well, I think we have all been there.

After having fish and after researching about fish and aquariums and the do’s and don’ts, I now understand a lot of things that I didn’t many years ago. The biggest most important thing that I have learned; when is it best to put fish in a newly set up fish tank! This information wasn’t available back in the ‘stone age’, when I first had fish.

So, how long do you have to wait before you can add fish to a brand new tank set-up? This could mean the difference of happy healthy fish that live a very long time, and fish that only last a week, or two. The optimum wait time varies depending on who you ask, what website you look on, or what a pet store employee tells you. The correct answer: 3-6 weeks!! NOT 15-30 minutes, NOT 24 hours. You need a full 3-6 weeks before adding any type of fish to the new tank.

You probably think that I have lost my ever loving mind. Some of you are reading this and saying, “3-6 weeks is ridiculous” or “there is absolutely no reason that you would need to wait that long”. There are many other statements and comments too, I’m sure. But yes, 3-6 weeks. We are going to give you all of the important reasons why you need to wait so long and what, if anything, do you do to the water in that time-frame and the proper way to introduce your fish to their new home.

Very Important Tips

I am giving you these tips so you know what NOT To Do after your initial tank set-up.

  1. Do not start with a tank smaller than 20 gallons. Certain water parameters change quickly in the smaller tanks, which leaves no room for any type of error during set-up and fish introduction.
  1. Do not add to many fish, all at once, when it is time to bring them home. If you add too many fish at one time, especially different species, there could be some fighting. It will also undo all that you have done in the time-frame, within a matter of days. Try to find fish that compliment each other and can cohabitate well together.
  1. Do your research, find out what fish can live together and what fish you definitely can not put in the same tank. Then you will start adding them, 1 or 2 at a time, when the tank is ready.
  1. Do not neglect the filtration system. The flow of the water through the filter is the element that makes the water safe. You also do not want to neglect the pH and other balances in the tank. There are inexpensive kits that will help you achieve and keep the chemical balances in your tank at just the right levels. 
  1. Make sure you have the best equipment possible. Having a fish tank isn’t cheap, especially if you are wanting something bigger, with exotic or tropical fish. So make sure you price check, budget, and save so that you are able to get the best necessities possible. The filter helps clean and circulate the water. If you have a cheap filter that gets clogged super easy, you are going to spend more time cleaning, and having fish funerals than enjoying your new pets. 
  1. Do very extensive research. Make sure you are getting the correct lights, filter, filtrations system, plants, and other accessories that are best suited for the fish you are going to keep in your tank. **This also goes for chemicals.** Is your water fresh or saltwater? There are going to be specific items for those specific types of water. 

Steps to Setting Up The New Tank

There are a few steps you need to follow to set up your new tank. Besides the obvious, taking it out of the box and placing it on the fish stand.

The first thing you need to do is rinse off all of the gravel that you are going to put in the bottom (or rocks, if that is what you choose), plants, and other decorations. Make sure you add the gravel slowly, and carefully as not to damage the bottom of the tank.

You can read this related article by clicking here: Set Up A New Aquarium For Beginners 

The second step is to fill your tank, use tap water or bottled water. Fill it slowly, so you do not disrupt the gravel.

*TIP: place a plate in the tank and pour the water slowly onto the plate to reduce the cloudiness, and the splatter*.

The next step is to turn on the filter and the heater if you purchased one. Leave your tank light off for the time being. The tank lights promote algae growth.

After you have your tank full, you are ready to add your treatments. Water conditioner and bio filter are a must. Read all directions carefully, so that you do not put too much (or too little in). This could hinder the process, and make it take longer.

Next, is one of the biggest and main reasons that you can not put fish in a tank right away. This part takes the longest, but provides the best results for your fish. Let the tank cycle. It will go through what is called “New Tank Syndrome”. This is going to create a healthy environment for your fish. So please be patient. This process will take 3-6 weeks.

In order to begin the cycle, you will need to add a very healthy pinch of fish food to your tank. This is going to break down into ammonia. It will also begin the start of healthy bacteria growth on the plants, gravel, and other decorations. You can speed this process up by a few days, if you have an established tank. Take a decoration or 2 out of it and put it in your new tank.

These will already have good bacteria on them and can help with the process of breaking down and getting rid of the ammonia, and other bad bacteria. 

Next Steps Is the Nitrogen Cycle

These are very important occurrences that need to happen so that you can add your fish, with no worries, to their new home. This is a slow process, but if you want your fish to last and be happy, it is a necessity.

Cycling is the process of good bacteria taking the bad bacteria and transforming it into non-toxic waste. Toxic waste is fish secretions, fish food, and any dirt or dust that gets into the tank. Most toxic waste is in the form of ammonia and can kill your fish if the levels get too high.

Kick starting, what is referred to as the Nitrogen Cycle, can take awhile. The good bacteria in your filter and gravel bed will begin to consume the ammonia and nitrates. Nitrates are not bad for your fish at a lower level and this is why the 20-25% water changes are recommended once a week, even during the cycling stage.  This keeps the nitrate levels down.

Live plants will actually aid in the cycling process better than the fake plants will. They also add a little extra boost of oxygen to the water, which can benefit your fish. Monitor your ammonia by checking your levels once a week, beginning with the cycling phase.

When the cycle is almost complete you will notice a spike in nitrite followed by a gradual increase in nitrates.

Make sure, during the cycling process, you do not add any chemicals that are made to remove or reduce ammonia. The good bacteria NEED the ammonia to feed. As stated earlier, if you have a tank that is already established, take some of the decorations and put them in your new tank. This will start a good bacteria culture, which will help reduce the cycling time.

Testing The Water and Adding The Fish

You can find a few good testing kits at any reputable pet store. Your ammonia and nitrite levels need to be at zero and your nitrate levels should remain below 40 ppm. Test your water everyday and make sure all levels stay consistent, through the cycling phase. This is how you are going to know when the cycling stage is coming to an end.

Sometimes it is difficult to acclimate your fish to the new tank. There are a couple of reasons why the fish could die, even after letting the tank cycle, shortly after putting them into their new home. 

  1. They were unhealthy to begin with. Be picky and check out the fish closely when at the pet store. If they look lethargic or like something isn’t right, then do not purchase any fish out of that tank. 
  1. It wasn’t acclimated properly.
  1. The levels rose for an unknown reason, meaning the ammonia or nitrate levels were too high for the fish to survive.

The proper way to acclimate your fish to a new tank is; turn down the lights (in the house). Lights can shock or damage the fishes eyes, if they are too bright. Keep the fish in the bag from the pet store, roll the edges down and set the bag in the water to float. 

Gradually add water from the tank into the floating bag, every few minutes. This should only take a couple of hours. Make sure you have a precise thermometer. Temperature is extremely important for the survival of the fish.

You want to keep your fish out of direct sunlight, especially if you have a heater in your tank. If you keep your house on the warmer side in the winter, depending on what the temperature should be for the fish you bought, you can get away with not having a heater.

Because your house temperature will keep the water at a perfect temperature for the fish. Never feed your fish more than they can eat in about 2 minutes. This will greatly reduce what falls to the bottom, causing bad bacteria and producing ammonia.

Start out with a small pinch. If they eat it within 30-45 seconds, you can give them another small pinch. Then you know, 2 small pinches of food and then you should not have too much falling into the gravel.

Remember to do your 20-25% water changes every week. This will get rid of any extra bacteria and things that are floating in the water, stuck in the filter, or lying on the bottom of the tank. They have some extremely nifty gadgets out there that can help you get this chore done in less than ½ an hour. 

48 hours before you do your water change, you want to make sure you are leaving the ‘new water’ in a pan or a bowl (covered) on the counter. This will ensure that the water that you are putting into the tank is the same temperature as the water that is already in there. Making sure that you do not shock your fish by adding water that is too cold. 


There you have it, folks, the answer to the question: How long do I have to wait to add fish to a new fish tank. 3-6 weeks. Seems like a long time, but it will go by quicker than you think. It will eliminate the cloudiness that new tanks go through, and it will eliminate the bad bacteria and build up the good bacteria giving your fish a nice clean and healthy place to come home too.

They won’t have to fight through the cloudiness, and the putting of chemicals in the tank and everything. Your water will be crystal clear, and in prime condition for your fish to thrive and grow from day 1. 

Just remember to do your research when you buy your tank, in order to get the best equipment and necessities, and then do your research while your tank is cycling. This will give you plenty of time to find the perfect fish for the tank, and maybe a couple different species that can cohabitate together very nicely. Giving your friends, family, and other house guests something peaceful and beautiful to see when they enter your home. 


I'm passionate about fish pets and love sharing everything I learn about them.

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