How Often Can I Add Fish To My Saltwater Tank?

Adding new fish to your saltwater tank is something that needs to be carefully planned out. Before setting up a new saltwater aquarium, you want to have a short and long term plan for stocking the tank properly.

Adding too many fish into your system can have huge consequences. 

It’s important that you add fish slowly over time and not all at once. There is no set limit for determining how many fish or how often fish should be added. Every system will be different. But as a general rule, you should plan to add only 1 new fish every 10-14 days. 

Let’s look into this topic further and I will explain why it’s so important.

Cycling Time And Adding New Fish

Saltwater nitrogen cycle

If your saltwater tank is new and being set up for the first time, your cycle will take approximately 4-8 weeks. Once the cycle is complete, you can add your first fish.

Make sure to use a good quality saltwater test kit to ensure the proper results. Some lower-priced test kits are very unreliable and will give inaccurate readings. 

You shouldn’t add fish before the cycle is complete. Also never use fish to speed up the cycle time. Many people will do this and it’s not only cruel to the fish but they can add an ammonia source that is too much for the system at the time causing huge concerns.

Saltwater tanks can take a long time to mature and it’s crucial that you let your tank naturally progress to being a healthy system. Nothing happens fast with a saltwater tank!

Bioload Will Increase When Adding New Fish

Fish tank

Each time you add a new fish into your tank, your bio load increases. It will take time for the biological filtration to catch up to the new biological load. 

Adding too many fish at once will not only cause a spike in bioload, but your water parameters will fall out of range causing many problems. It’s possible for your tank to go through another cycle which can be very harmful to your fish. So the 10-14 day waiting time in between adding new fish will help prevent a large spike in bioload over a short amount of time.

Quarantine When Adding New Fish

If you have a proper quarantine tank set up (which I suggest you do), your new fish will go through a 2-4 week quarantine then moved over to the main tank. Since the quarantine time is longer than the general rule of thumb for adding an additional fish, you are safe to add another fish to the QT. 

If your plan is to have 5 total fish in your tank, then it should take you about 10+ weeks to have them all in the tank together. 

If you are not using a quarantine system, then you can add an additional fish every 10-14 days. I recommend you check your water parameters on a regular basis to ensure Nitrite, Nitrate, Ammonia levels are in the proper range and your tank is not going through a cycle. 

Also without quarantine, the extra time in between adding fish will allow for any diseases from the new fish to show up. You wouldn’t want to add another fish to the tank if the fish you just added was carrying a disease.

Time For New Fish To Acclimate

Another reason for waiting the 10-14 days in between adding new fish is this will give plenty of time for the new fish to acclimate and get used to its new home.

This will also allow time for other fish in the tank to adjust to a new tank mate keeping stress at a minimum. There are times when you may need to add a couple of fish at the same time due to aggression but in the case of adding 1 fish at a time, you should wait 10-14 days in between.

If your tank is well established and healthy, you can get away with adding additional fish in a shorter amount of time. I still recommend every fish go through a quarantine period first before being added to the main tank regardless if your tank is new or many years old. 


So waiting for the 10-14 days between adding a new fish to your tank is very important. This can eliminate a huge headache for you. There will be a much better chance that your tank will stay cycled and all water parameters will remain within limits, your fish will have plenty of time to get used to its new environment, other tankmates will get used to the new fish, and any parasites or diseases will have time to show up before you add another fish. All of these are great reasons to space out the time between adding any new livestock to your tank.