Do I Need To Change Water In A Filtered Fish Tank?

With a variety of aquarium filters that are available, you might wonder if partial replacements of water in the tank are still a necessity.

In general, you should regularly replace the water in your aquarium, even if it has a good filter installed. Any given filter does not take care of all aspects of cleaning. You have to remove nitrate from the tank and that is accomplished by replacing water. Removing some of the waste also prevents the filtration system from getting overwhelmed and you have to do less maintenance of your filter.

Consider the basic functions of the three different types of filters.

What Does The Filter Do For Fish Tanks?

Aquarium filters remove excess food, decaying matter, particles, chemicals, and by-products of fish activity. There are three kinds of filters and each addresses water quality using different mechanisms and principles.

Biological Filter

A biological filter is quite essential because it uses the right kind of bacteria to convert ammonia and other toxins into more tolerable substances, such as nitrate. Ammonia is one of the by-products of fish activity and its production is constant. If not removed, it accumulates and causes stress to the inhabitants of the aquarium. Eventually, it could poison and kill fish.

Nitrate is harmless in limited amounts. It does, however, still need to be removed from the tank, and that is one of the reasons changing, or partially replacing water, is still important.

Chemical Filter

A chemical filter uses activated carbon to remove toxins from the water. The principle is the same as when a physician prescribes it to a patient to reverse poisoning.

Chemical filters work well if there is sufficient water flow in the tank. This type of filtration is important if the water you use, usually tap water, is known to have a lot of chemicals in it. Most treated water is too harsh on fish and at the very least needs to be dechlorinated.

If you are just getting ready to set up a new fish tank, you could leave the water exposed to sunlight for a day or two, ideally for a few days. UV light dechlorinates water but the natural process takes a few days.

Mechanical Filter

A mechanical filter uses a sponge or a net to physically remove debris, and waste and prevent the water from becoming cloudy.

Mechanical filters require some maintenance to be effective, and that includes regular cleaning or replacement of the filter cartridge. There needs to be some flow of water in the aquarium to make sure that all water goes through the filter.

What Does A Partial Water Change Do?

Even if you are using two or three kinds of filters for optimal maintenance of water, you still should replace 10-15% of the water every week. The practice of replacing water diligently takes care of several issues, thus completing the task of keeping the water in the aquarium optimally pure for your fish.

When ammonia is converted to nitrate, it must be removed from the tank regularly before it accumulates to unsafe levels. Neither kind of filter can do the job effectively but replacing the water partially reduces the amounts of nitrate in the environment of your fish.
Even if you use a good filter, it cannot always maximize filtration. If the flow is limited or if the fish sometimes produce more waste that the filter did not catch, the habit of your pet fish could become toxic and dirty. Replacing the water on a schedule helps fill in any gaps, so to speak. There is less chance for the buildup of toxins if the water is changed as well as filtered.
If you use a mechanical filter, it will require less maintenance if you help the system keep the water clear. Chemical filters also work better if there is not too much waste in the tank they have to tackle.

Never change a large portion of the water at once. Changing over about 25% of the water suddenly could alter the environment dramatically. The stress of the rapid change could be enough to kill some aquarium pets. Never change the entire water in the aquarium all at once.

Changing The Water Without Disturbing The Fish

The general recommendation is to change 10-15% of water about every week. If you have a large tank, you could change larger portions of the water less frequently.
You could dechlorinate water before adding it to the aquarium. If you use a chemical filter, it is okay to add the water as is.

Ideally, bring the water to approximately the right temperature before adding it. If the water could be much colder, add a smaller amount at a time to prevent excessive stress on the fish.
Use pH strips to check the acid balance in the water of your aquarium once in a while. Even with proper filtration and cleaning routines, it is good to catch a problem early on if there is one.
Add the water very gradually. Your fish will probably hide while you are doing it.

Clean some items, not all at the same time, either when replacing water or on a separate schedule.
Remember to wipe the interior walls of the tank with a sponge.