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When I search the internet about this question there are many different opinion about the right interval to change filtration media in a regular freshwater tank.

On the packaging of different media filter, the interval to change the media seem to vary by a good amount. Of course, company producing filtration media are more interest to make profit than what is left in my pocket, so for them the more I change the media the better.

So far, I have never changed the filter media of my filter. About once a month I will take apart the filter and clean it in old water tank (from a water change). I will clean the sponge covering the intake (I got shrimp so no baby in the filter) than the different media from the filter (another sponge, a bag of small rock and the charcoal bag). To clean those parts, I rinse them gently in the water until there is not much coming out and then put everything back together.

I'm not really interested to ear about the charcoal since after about two weeks it don't really have any effects on chemicals but since I don't use any in the tank I don't need to have any filtered out.

So why should I change (or not) my filtration media?

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In a traditional freshwater aquarium filter, there are three separate parts: Mechanical, Chemical, and Biological

Mechanical: This is your top sponge, it just filters out particles in the water such as uneaten food or fish waste. The people that sell fish pads are going to tell you to change it every two weeks, but you should be fine changing it every month or two depending on how dirty it gets. As long as you are washing out the particles that collect in the sponge, use it as long as it will last. A good rule of thumb is if the sponge has turned dark brown/ black and remains so after a rinse - its time to replace. Also, if it is falling apart or you can easily tear it apart it is time for a change. A fresh sponge is important to collect the maximum amount of particles from the water to keep it clear and fresh for your fish.

Chemical: This is the charcoal that removes toxic substances such as airborne contaminants from the water. It is really just to make sure there is nothing offensive to humans in the water, but I change mine two or three times a year just to be safe.

Biological: These are the "rocks" at the bottom of your filter. It encourages the growth of special bacteria that process ammonia and nitrite and convert these materials to relatively harmless nitrate. This keeps the biological balance in your aquarium. Do not replace this unless you are setting up a new aquarium as it is dangerous to your fish and could cause them to die.

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  • Your answer do a really good job explaining each part of the filter but it doesn't answer my question (Why should I change those). You kind of answered the part about the biological (never change it) and my question has a link the the chemical part. So why should I replace my mechanical filtration vs just cleaning it? – Rémi Dec 18 '15 at 19:15
  • Well, cleaning the mechanical should work just fine. But eventually you will start to notice it loses it's quality and that is when you should replace it. You will notice the coloration of the sponge getting dark and that means that less "stuff" is getting caught in the sponge because there is less room in it to catch things. A new sponge every month means a fresh start so you can make sure the maximum amount of excess food and waste is caught. – MSU_Bulldog Dec 18 '15 at 19:21
  • Did this answer your question? – MSU_Bulldog Dec 18 '15 at 20:10
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    It kind of did, I would have liked something a bit more scentific than "when you notice" but it still better than nothing :) If you can edit your answer to include those information I will mark your answer – Rémi Dec 18 '15 at 20:25
  • I added some more information to the mechanical part of my answer. When in doubt, change it. Better to have a super clean tank than risk letting it get dirty. Once the sponge is done, the tank will quickly get really dirty. – MSU_Bulldog Dec 18 '15 at 21:24

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