When to Change the Filter in a Fish Tank

The most typical queries from first-timers are mostly related to fish tank filters. When to change the filter in your fish tank and how often? Are fish tank filters necessary at all? Which one should I use? Fear not, here is a complete guide to all your filter-related questions. 

If you are a die-hard fish lover, then the chances are that you already have a beautiful aquarium all set up in your home.

You must know the routine of maintaining your tank inside and out but what about those of you who have just decided to get one? Worry not, it’s easy to learn everything you need to know, so let’s get started!

When to Change My Fish Tank’s Filter?

aquarium filter setup

Internal filters usually have a longer life and you can keep the same sponge for months before changing it.

External filters need to have their media changed once per month or sooner if the water becomes cloudy or the filter media is falling apart.

How often to replace internal filters media?

When it comes to a regular sponge in an internal filter, I have to admit that I usually set and forget them. As long as the sponge is intact and you clean it properly ever couple of weeks or so, it’s good to go.

Changing the sponge too often is not beneficial to your fish tank. That is where most beneficial bacteria live and removing them regularly can result in destroying your aquarium’s water balance.

This is why it’s best to keep the replacement sponge in the tank’s water for a few days before prior to changing the old one. This way, it will be populated with at least some of the beneficial bacteria that will be removed.

But usually, instead of simply replacing the sponge, giving it a good rinse when doing a water change is all that you need to do.

Make sure you clean it in the water you remove from the aquarium and never chlorinated water (as it will kill the beneficial bacteria living there).

How often to replace external filter media?

When it comes to external filters that have multiple layers of filtration, things change a bit and replacing the said media should be made more often.

Especially for external filters that use activated charcoal for filtration, that media should be changed ever three weeks or so.

Other media should also be changed based on their performance and age. But usually it’s the activated charcoal that loses its power after a few weeks and needs changing.

In conclusion, for both types of filters, your observation skills and common sense come into practice. If the filter is not performing properly, it needs at least a proper cleaning – if not a complete replacement of all or part of the media.

Subsequently, there are a few signs you can look out for which can tell you exactly when you need to change your filter:

  • The water has become cloudy and dirty 
  • When the biological media starts to slow the flow rate noticeably
  • Your filter media is falling apart, or it seems choked

Just remember: in most cases, you don’t have to change the filter, but clean it. Rinse it well in the water that you have removed from the tank (or at least use dechlorinated water) and you’re all set to go!

Do I Really Need a Fish Tank Filter?

how often should we change aquarium filter

Yes you do! Can you breathe properly in polluted, dirty air? How can your delicate fish breathe in dirty, toxic, and contaminated water?

An aquarium is supposed to provide an aura of calmness and serenity, so how would a dirty fish tank look in your home or office?

The filtration system in your fish tank is necessary for the health of your fish and providing them with the proper environment.

The filter not only draws in all the debris from the fish tank, but also helps beneficial bacteria grow, while moving the water continuously, so it doesn’t get that stale water smell.

Without a filter, you still can prevent the water quality to drop significantly by doing more frequent water changes.

But if you do it too often, you will destroy the balance of the water itself, while frequently changing the water in your tank gets old really soon – and the larger your aquarium, the more daunting of a task it is.

That’s where a fish tank filter comes in. All you need to do is set it up and clean it instead of the whole aquarium. From a safety point of view, here is why you need a fish tank filter: 

  • To remove debris, decaying organic matter, fish waste, and excess food accumulating in the water
  • To prevent ammonia poisoning of the fish due to the presence of excess waste and toxins
  • Removal of bacteria and other dissolved organic matter
  • To keep the water clean and provide ample surface for oxygenation

If you want to get a bit more in depth on this matter, I have a dedicated article written, explaining what a filter does in a fish tank.

How to Install a New Filter

Before installing a new filter, you must know about the type of filtration method being used in the aquarium and it usually depends on two major factors: whether you have an external filter, or an internal one (with a sponge).

For instance, you can change the mechanical portion of the filter whenever you like. But when it comes to chemical or biological filters, the filter can be changed once the filtering process has occurred.

We have a complete guide on installing an aquarium filter here. But, for the summary you can just read below.

The key to changing your fish tank filter is to make sure that you don’t lose the beneficial bacteria in the process. The following are some easy ways of installing a new fish tank filter without losing the bacteria:

  • Leave your old filter media with the new one for about a month for the cultivation of bacteria.
  • Put the old filter’s media into the new filter, which is of the same size and shape to prevent the loss of bacteria.
  • Colonize the new filter by simply putting the old filter’s media next to the new filter for about a month if you can run two filters.
  • If it is a sponge, simply place it in the tank’s water for a week or two, so that the beneficial bacteria colonize it.

Now you know everything you need to know about when to change filter in fish tank to keep all your finned friends happy and healthy!

But if you have additional questions, don’t hesitate to ask them below.

Share the article below:

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.