How Long Can Beneficial Bacteria Survive Without Fish?

Last Updated on March 29, 2022 by cmoarz

This question comes up once and a while, usually when people need to keep their tank empty for a bit while they move or go on vacation but want to know if the tank cycle will survive.

Bacteria need ammonia as a food source to survive, But if there is nothing in the tank to produce that ammonia, how long can beneficial bacteria survive without fish?

Will beneficial bacteria die without fish?

There are only 2 states to nitrifying bacteria, dead or alive. Most types of nitrifying bacteria we have in our aquariums do not go dormant when it doesn’t have food, but that doesn’t mean it dies either.

In fact, there are a lot of ways to kill this good bacteria really quickly, including drying, freezing, boiling, chlorine, But when it comes to starvation, it can take a very long time.

So how long does beneficial bacteria live without fish?

How long? A study done by R Wilhelm discovered that beneficial bacteria can survive for over 1 year without ammonia or fish present to feed off of. So no, beneficial bacteria won’t die without fish for at least 1 full year.

So what does that mean?

It means not much is going to happen to your tank in the short term if you go on vacation and don’t have fish for a week or 2. The bacteria will still be there, waiting for you to come back and add some new friends.

How can we keep beneficial bacteria alive without fish?

So we’ve established that starving the bacteria to death takes a long time, but what about the other factors that can kill the bacteria off really fast?

Well, Keeping the bacteria alive doesn’t take much-concerted effort on your part in this case. As long as the filter stays submerged and wet and doesn’t freeze and you avoid any chlorinated water sources (use dechlorinator).

This pretty much amounts to your usual temperature control. If you turn your heat off completely while you are away, consider using an in-tank heater that will keep the water temperature at a steady state.

Keep the filter running the entire time you’re away and have a cover securely attached to the top of the aquarium to keep evaporation to a minimum.

These are all just precautions to take so that you don’t have to worry about your tank while you’re gone. The bacteria will still be there when you get back, happy and waiting to be fed again.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!