How Often To Change A Fish Tank Filter And Media – Full Details

    How often to change a fish tank filter and media

    To keep your aquarium properly maintained you should know how often to change a fish tank filter and media. The filter is the life support system for your tank and keeps it looking crystal clear. If it’s allowed to grow clogged, fish health will suffer.

    As a rough rule of thumb, mechanical and chemical filter media should be changed every few weeks. And biological filters never get changed; just rinsed if they grow so clogged they impede water flow.

    But there are other circumstances that affect this schedule. So allow me to share a few tips on how often should you change your aquarium filter!

    How Often To Change A Fish Tank Filter And Media – Main Factors

    How often to change an aquarium filter
    Common goldfish (Carassius auratus)

    I covered a general maintenance rule above that applies to most aquariums. That said, the type of filter you have and the fish population also affect how often you do maintenance on your aquarium filter!

    Fish Tank Filter Type

    The first factor affecting how often you should change your aquarium filter is the type of filter you have. Different filters have different maintenance schedules.

    Sponge Filter Maintenance

    An aquarium sponge filter is the simplest kind. They are a large sponge that screens out particles and provides some space for beneficial bacteria to live. Sponge filters used on crowded tanks may need to be squeezed free of debris weekly. A process that only takes a few minutes.

    Power Filter Maintenance

    A power filter is more advanced. It typically has cartridges that contain cotton floss and carbon. These cartridges need to be replaced biweekly in most aquariums.  Power filters tend to use proprietary cartridges shaped for the unit.

    Canister Filter Maintenance           

    Canister filters are the most flexible since they are designed so you can use any kind of media you want! If you have an ammonia removing agent, it may need to be recharged weekly. Activated carbon gets replaced biweekly, as normal. As does cotton floss.

    Canister filters also have flow adjustments, affecting how much water is processed. Which in turn, affects how much material you need to be changed.

    Have you decided which type of filter is right for your tank? If you’re considering an upgrade to a new unit, this video breaks down the benefits of the many different kinds of fish tank filters!

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    Aquarium Fish Population

    Your aquarium fish population is even more important than the kind of aquarium filter you have. Fish are the source of all water pollution.

    Any leftover food decays into ammonia if not collected during a water change. And fish poop transforms into tank water pollution over time.

    The more fish you have the more maintenance you have to do. You can use a more powerful aquarium filter to reduce some of this load. Many aquarists will even use two or three filters on a heavily stocked tank.

    But three filters still means three units to maintain since you have so many fish. I always recommend under stocking an aquarium whenever possible.

    Fewer fish means less tank water pollution and a healthy aquarium. It means your single filter will run more effectively, which means less work for you. And your fish have more space to roam!

    Maintain A Maintenance Schedule

    A fish tank filter needs to be maintained through regular cleaning and changing of the media. Since each filtration stage has a different lifespan, you need to be aware of what has been done. And what can be left alone and handled at a later date.

    For example, you may want to replace your mechanical filters and chemical filters biweekly. And once every six months gently clean your biological filter. All of this changes when you start using specialty mechanical or chemical filters, which may get used up very fast.

    If you are a beginning aquarist, I recommend using a schedule or sticky notes to keep track of the maintenance you’ve done in the past.

    Types Of Fish Tank Filtration

    Dwarf Puffer (Carinotetraodon travancoricus)

    Aquarium filters come in an endless array of models, designs, and price points. But they all rely on these three ways of purifying aquarium water!

    Mechanical Filters

    Mechanical media is the first barrier that water comes into contact with when it enters your aquarium filter.

    Mechanical filters are the simplest kind of filter media. They are physical barriers to particles floating in your aquarium water. Assuming the particles are the right size, they are trapped by the mechanical filters and held there.

    The most common kind of mechanical filter media are cotton pads. They screen out large to medium sized particles, depending on how finely woven the mesh is.

    Eventually the filter floss becomes clogged with fish waste, leftover food, and other large particles. It then needs to be changed out.

    A mechanical filter needs to be replaced monthly in most fish tanks. Otherwise the clogged media will start to prevent water flow through your aquarium filter.

    Aquarium mechanical filter media can be purchased in large rolls. You then cut them to fit the media chamber of your power or canister filters.

    Diatomaceous earth is a special kind of mechanical filtration. It consists of the skeletons of microscopic diatoms that are millions of years old.

    Diatomaceous earth is so fine that it will screen out green water algae, fine dust, and other particles too small for filter floss. It clogs much faster, though, since it catches almost all particle sizes. So be ready to change it as needed.

    Chemical Filtration

    Chemical filter media is the second stage of filtration that water encounters in your aquarium filter. Once water has been screened of floating particles it passes over agents that chemically react with dissolved impurities.

    The kinds of chemicals removed from the water depends on the type of chemical filters being used.

    The most common kind of chemical media is activated carbon. Better known as charcoal, it’s used in nearly all aquarium filter designs due to how effective it is.

    Activated carbon is wood that is heated to very high temperatures. Next it is broken into small granules. Which not only to make it easier to fit into a filter bag. But also increases its surface area, which is crucial for how effective a material is at adsorption!

    Activated carbon adsorbs to dissolved organic molecules like proteins and tannic acids (from plants and driftwood). It also removes chlorine and chloramine.

    You still want to use tap water treated with water conditioner for refilling a fish tank, however. Activated carbon won’t work fast enough to save your fish from a lethal dose.

    Activated carbon won’t remove nitrogenous waste products (ammonia, nitrite, and nitrate). But there are chemical filters that do bind to these agents, including zeolite resin.

    There is a tremendous variety of chemical filter options for aquariums. They are ideal for a canister filter since these aquarium filters have extra space for custom additions. You can target phosphates, dissolved minerals (hardness), and other chemicals.

    Like mechanical filters, most chemical filters get used up over time. Some can be recharged, like ammonia or salt removing resins. But most need to be replaced every 2 to 4 weeks.

    Biological Filtration

    Biological filtration is the third time of filter media found in any effective aquarium filter. It operates by providing a home for your beneficial bacteria to live. These nitrifying bacteria feed on nitrogenous waste products.

    Ammonia and nitrite are the two most dangerous water pollutants for fish. But beneficial bacteria feed on these chemical impurities, converting them into nitrate, the least dangerous form of nitrogenous waste.

    Nitrate then collects in your aquarium water until removed through water changes. Or it is used as food by live plants or algae.

    Bio media is a physical home for bacteria to live in. Most are hard, rigid substances that won’t dissolve in water.

    Plastic, lava rock, and ceramic rings are a few common kinds of biological filters. The smaller the pore sizes the more surface area they provide for beneficial bacteria.

    Most types of biological filter media does not need to be replaced. Once in a while you may need to rinse it if your bacteria colonies grow too thick.

    This can prevent proper water flow, causing water to bypass sections of the filter. But that only needs to be done at most once every 6 months.

    How To Maintain A Fish Tank Filter And Media

    How to maintain a fish tank filter and media

    Once your filter is clean and running, how can we keep it that was for as long as possible? As always, prevention is the best medicine for reducing time spend changing filter media!

    Feeding Properly

    One of the best ways to reduce how often you need to work on your filter is to feed less. Most aquarium hobbyists feed their fish far more than they need to. Overeating is as bad for fish as it is for people. Fish can get fat and it reduces their lifespan.

    An even bigger problem is the impact of all that extra fish poop and leftover food on water quality. When these agents drop into your substrate bacteria decay them into ammonia and nitrite.

    Your nitrifying bacteria will handle most of this. But a sudden burst of pollution can overwhelm them. Causing stress or even death in your aquarium fish.

    So how often should we feed our fish? Two or three times per day is enough for all aquarium fish. Don’t be taken in by their begging every time you walk by the tank.

    Even when full, fish will still eat what you offer them. Their wild instincts tell them to eat whenever food is around. In the wild, food may not come around for several days. Therefore, it’s better to be fat for those lean times.

    The amount per feeding is also important. For small to medium sized fish, go by the size of their eye. A fish’s eye is about the size of their stomach (less true for larger fish). So offer enough food to fill that amount of space!

    Live Plants

    Live plants are one of the best things you can add to an aquarium! They work as hard as your fish tank filter at maintaining good water quality. Plants act as biological filters by using nitrogenous waste as fertilizer.

    Plants also consume carbon dioxide and release oxygen, aerating the water for fish. They also create shade, helping fish to feel safe and competing with algae for light.

    Live plants won’t replace a filter for good unless you design the tank specifically for that purpose. Walstad aquariums can use plants as your only filter! But they are designed specifically for this purpose and are intermediate to advanced level systems.

    Does Changing The Filter Remove Beneficial Bacteria In The Tank?

    Rainbow fish (Melanotaenia boessemani)

    Changing the filter media does remove small numbers of beneficial bacteria from the system. But the overall amount removed is tiny so long as you only change the mechanical and chemical media.

    Changing the biological filter media is not something you should ever do. That is the permanent home of your nitrifying bacteria. It never goes bad. At worst, it will grow thick with bacterial growth.

    The bacteria live everywhere in your tank but are found in the highest numbers in your filter and gravel.

    Some of it can be rinsed away if it’s impacting your water flow. But throwing it all away partially resets your aquarium nitrogen cycle. This may lead to an ammonia spiral and crash called new tank syndrome.

    Once new tank syndrome sets in it can be very difficult to correct. Filter maintenance is important but don’t go overboard and try to keep it spotless!

    If you do suffer a crash, you can correct this by adding a batch of live bacteria to your tank water. Products like API Quick Start instantly re-cycle the tank for you.

    By adding some to the tank water they will work immediately on ammonia. And start recolonizing your tank, preserving fish health!


    Knowing when to remove old filter media is part of keeping a fish tank clean and healthy. But not all media needs changing. You can even over-change biological filters, causing the tank’s nitrogen cycle to crash.

    Stick to removing filter pads and carbon through a regular cleaning schedule! And adjust that as needed for specific media choices like diatomaceous earth or ammonia absorbing resin.

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