Adding Fish to Your New Aquarium

Now that you have waited at least 24-48 hours after setting up your aquarium, it is possible to add fish. If you haven’t read about the nitrogen cycle, we recommend you do that now.  

You can add fish immediately and allow your new fish to start the nitrogen cycle on their own or you can start the nitrogen cycle before you add fish by adding an ammonia supplement. This article summarizes both processes. 

  1.     Fishless Cycle

Fishless Cycling has quickly become a popular method for starting a new tank, because it reduces the chances of losing fish in the process. Fishless cycling can be achieved by ghost feeding or ammonia supplementation. Ghost feeding is achieved by adding fish food to your fishless aquarium. This allows the fish food to break down in the water and introduce ammonia which feeds the bacteria for your cycle. Alternatively, you can add ammonia, such as Peter’s Bacter Feed.  Bacter Feed raises the ammonia level in your tank. Adding Tank Buster and other bacterial supplements, allow the bacteria to convert the ammonia to harmless nitrates. Fishless cycling usually takes an average of 2-4 weeks. 

Learn more about using Peter’s Bacter Feed here.

  1.     Fish Cycle

Simply adding fish the first week is by far the most common way to start an aquarium. Start by introducing 10-20% of the total fish allowance for your aquarium. This will ensure ammonia and nitrite spikes are more manageable and less likely to harm your fish. Cycling your tank with fish is typically a 4–8 week process. We recommend choosing hardy fish to start out with. Consult with a Pisces Associate for advice on which fish make good first time additions. During this process, test your ammonia, nitrite, and nitrate daily. Do not let ammonia or nitrite exceed 1ppm. 

Your cycle is complete when ammonia and nitrite have returned to 0ppm, nitrate will usually be around 20ppm - if it is 40+ppm do a partial water change. Even though your cycle is finished, continue to add fish slowly so the bacteria can keep up with your fish’s waste. 


Whether you are adding new fish to an established or brand new aquarium, it is important to acclimate you new fish to their environment:

  •       Turn off your aquarium lighting, this will help reduce stress. Keep lights off for at least 2 hours, 24 hours is ideal.
  •       *Float the fish in their bag, unopened, for 20-30 minutes to allow the water temperatures to match.
  •       Gently net your fish out of the bag and into the tank. 
  •       DO NOT allow water from the bag to mix with your aquarium water.
  •       Add Peter’s Step 2 and Tank Buster as directed on the bottle.
  •       Offer food – new fish may not eat for a few days after entering a new tank, but the addition of food will help keep current inhabitants distracted while your new fish adjust to their environment.  
  •       After 24 hours, test your aquarium’s ammonia level. Treat as required with Peter’s Tank Buster or a small water change.

*Some fish and invertebrates are more sensitive and should only be added to established aquariums. If you’re unsure about the requirements for the fish you’d like to keep, how to acclimate them, or need help with cycling your tank, give us a call or visit us in store!

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