Home Aquaria How to Change Fish Tank Water & How Often

How to Change Fish Tank Water & How Often

Aquariums need regular partial or complete water change mainly to remove dirt as well as to maintain balance and freshness. Owing to the fact that fish cannot survive in the absence of water, it is important that water substitution is done carefully to ensure your fish is alive, safe and healthy.

Read on to learn how to change the water for small and big tanks with or without siphoning, how often the water should be changed for various salty and fresh water fish, why regular replacement of water is necessary and tips to keep your tank clean and fresh.

How to change Fish Tank Water without Killing Fish

This process can be done either by completely emptying the water in the current tank and replacing it with new water or by changing a percentage of the water already in your tank; usually around 10 -20%.

The first option, as you may have already guessed requires the fish to be taken out of the aquarium. It is usually not the best option since sudden change of environment can result to a shock which will eventually lead to stress.  If it must be done, then it should be when it is really necessary.

Following are the steps to replace the water.

Step 1: Get all equipment ready

Acquire all the necessary tools for the job. They include:

  • Magnet or algae pad
  • A 5-gallon bucket
  • A siphon gravel-based vacuum
  • Thermometer
  • Water conditioner
  • Water testing kit
  • Water heater
  • Detergent
  • Scrubber

Step 2: Prepare new water for the aquarium

This involves pretreating the new water. It helps in regulating the water temperature, PH level, ridding toxins, chlorine and other unwanted chemicals that do not sit well with fish. It is appropriate that you perform this the night before.

Fill your bucket (size/amount of water will depend on your aquarium) with water then add the water conditioner and allow it to settle overnight.

As the water settles, the conditioner does away with dangerous chemicals and metal residue in water making it safer for fish to thrive in. In addition, the conditioner introduces particles that adjust the water pH level.

During this time, water will attain room temperature and minimize the chance of exposing fish to cold conditions. In case the temperature is not the right one, do remember to adjust it so that it can be similar to the one in current tank.

Step 3: Tank Preparation

Your safety comes first in this step. You want to avoid unnecessary hazards such as electric shocks. Using dry hands, first disconnect any attached lightings and/or unplug any exposed heating elements in the tank.

Air Filter

Do remember to check the unplug and inspect if the air filter is working as it should.

Normally the components of the filter (cartridge, sponge etc.) stay clean for a substantial amount of time. They do not require cleaning as often as the tank water. If you replace it, a lot of bacteria would be removed thus upsetting water chemistry and would result in shocking the fish.

Rinse the filter using the recovered bucket water. Never use tap water since chlorine in the water will kill essential bacteria hence you will need a fresh nitrogen cycle.

 However, sometimes it may be faulty thus a replacement will make sense.

Plant & Decorations

Harmful bacteria, food remains and dirt I most cases attach themselves to the artificial items and plants in your aquarium giving them a sludgy appearance and eventually making them both harmful for your fish.

Take them out of the tank and clean/scrub them thoroughly using plant cleaning detergent and a scrubber. a very dilute mixture of beach water with a scrubber can still work. You can use 1-2 tablespoons of bleach for every bucket of water.

Finally, using the magnet or algae pad, run it on the side glass while scrubbing using minimum force. Also scrub the outside of the tank using designated solutions that are safe for fish. Fumes from unsafe detergents could harm the fish.

Step 4: Siphoning Water and Cleaning the Substrate

If you are doing a partial change, you can now begin siphoning water out of the tank to a separate bucket. You can as well use an automatic water changer.

Ensure you take out about 15% of the used water in your aquarium. Changing too much water, let’s say more than 30% can result in a change in the chemistry of the tank which will definitely distress the fish

For a complete tank water change, take a bucket of used water from the tank and put it another tank. scope out all the fish and place them in this tank. This will serve as a temporary aquarium as you change the remain water in the old tank. This procedure works well for small tanks.

If you are dealing with huge tanks, it is recommended that you use an automatic water changer. It will make your work easier, quick and safe.

While manually siphoning out the used water (in both partial and complete change) begin with placing the siphon tip into the tank’s substrate at the bottom, like gravel or sand.

This way, the siphon will pull out both debris and tank water. Do place the siphon into different areas of gravel to clean the tank for a thorough cleanse.

In case you have small fish and you feel like you risk sucking them, never use worn-out stockings at the end of the siphon. Ensure the mesh is large enough to accommodate debris.

Step 5: Add fresh water to the aquarium

Confirm the water temperature using the thermometer before adding it to the aquarium. Drastic change in temperature could end up killing the fish. Refill the aquarium when you are comfortable with the temperature.

Avoid refilling the new water in too fast and too aggressively. This can disorganize the gravel layer as well as the decorations.

Ensure you leave space between the water and the tank top to enable gaseous exchange.

6. Replacing decorations and plants

In case you took out any decorations and plants, do put them back. You can choose to place them on the exact positions where they were before or this can an be opportunity to come up with a new re-arrangement. The fish will probably appreciate your efforts. The choice is yours.

7. Reconnect

Dry your hands and connect back the filter, heaters and lighting. Take sometime to ensure that everything is working properly. If you did a complete change, put the fish back!

Changing fish tank water without a siphon

You can also change the water in the aquarium without using a siphon. Apply the above steps but instead of using a siphon, scoop water from the tank manually.

Ensure you only remove 15% of the water to prevent creating a chemical imbalance in the aquarium.

How often to change Water in Fish Tank?

The frequency will depend on a couple of factors. However, most aquarium owners agree that once in a week for partial change is fine for small tanks. For a complete change, you’d want to do it less frequently, probably once in one or two months. on many factors. Change 10 to 15 percent of the water each week.

It is important to change your aquarium water weekly; this would be enough to keep the fish happy and healthy. However, there are times when you will need to change the water more frequently, such as when you need to encourage fish growth.

It may be necessary to change the water frequently when treating or medicating the fish. Clean water aids in faster healing of fish. Frequent changes help reduce troubles related to aquarium water.

Factors that determine the frequency of changing Aquarium water

The frequency of cleaning a fish tank is dependent on various factors. Some signals will help you determine the appropriate time to change the water. The factors include:

Number and Size of Fish

Smaller tanks with many fish, will require more frequent water changes than larger, sparsely stocked aquariums.

Type of Change

If you doing a partial change on small thanks, the frequency can be higher compared complete change with big fish tanks

Tank Setup

The aquarium needs to be cycled up to enhance the health of the fish. The purpose of cycling up is to convert ammonia to nitrites then nitrates. You must control the nitrate level or else the fish could end up dead.

Water tests

These tests affect the number of times you will change aquarium water. When the ammonia, nitrate, or nitrite values have spiked, this is an indicator that water should be changed.


In case the water tests present high ammonia and nitrate levels, then the aquarium requires frequent water change. You will have to change the water until the levels reduce.

Hospital Tank

When your fish is sick, you will need to administer medication and change your water changing frequency. Some illness might force you to change the water daily.

Amount of Nitrate and phosphate in water

When you spot phosphates and nitrates in the aquarium, you will have to change the water frequently. Exposure to phosphates and nitrates results in diseases and may end up stunting the growth of fish.

You also need to maintain water chemistry stability.

Standard Water change

It is recommended that you replace 20% of the water to keep the fish in a healthy habitat. This helps maintain substrate and nitrate levels to a minimum.

Benefits of changing Aquarium Water

According to Caroline Golon, a professional aquarium expert, changing water in the aquarium regularly helps maintain balance by diluting harmful chemicals, removing toxins manually, and replenishing the essential elements. Regardless of whether you have salty water or freshwater aquarium, water change is vital and offers the following benefits:

Reducing Nitrogen-based pollutants

Nitrates, nitrites, and ammonia are nitrogen compounds that often harm fish. By employing biological filtration, you can convert ammonia to nitrites then to nitrates. Fish can tolerate low nitrate concentration, however, when it builds up, it ends up stressing the fish.

Continuous exposure to nitrates exposes fish to diseases resulting in stunted growth and death. Changing water reduces these pollutants resulting in healthier fish.

Removing decomposing organic material

Constant removal of decomposing matter in the aquarium has numerous benefits to the fish and aquarium.

Changing water ensures that nitrogen-based products, phosphates, and chemicals never result in poor water quality and clouded water.

It also maintains water pH since the chemicals tend to create an acidic environment.

Improving water Clarity

Regular water change aids in eradicating discolorations and foul smell in the aquarium. Besides, it improves the magnitude of light thus improving the growth of plants in the aquarium. Changing the water will ensure the water is clear and light penetrates through your aquarium.

Replenishing essential minerals and trace elements

Essential minerals and trace elements always get depleted when fish consume them. Changing your aquarium water will provide the fish with these elements thus enhancing the growth and coloration of fish. It also helps maintain suitable salt concentration.

Saving Money

Changing your aquarium water can eliminate the possibility of incorporating a filtration system to the tank. Through consistent water change, you will end up extending the fish life and save a lot of money.

Controlling Algae

Regular change of water helps keep algae in check. Algae are known to feed on built-up nutrients in the aquarium; therefore, eliminating the nutrients deprives them of nutrition. This will help prevent an algae outbreak in your aquarium.

Tips & Hacks to Keep Your Fish Tank Water Clean

Following are some maintenance tips to make sure your aquarium is fit for the fish living in it.

  • Do a regular water test the water for nitrate, nitrite, pH, carbonate hardness, and salinity (saltwater only). If these parameters are not in the right levels, the fish’s lives will be in danger.
  • Service the filter
  • Do not overfeed
  • Do not overstock as this will lead to more waste
  • Add active carbon to your filter to improve water clarity as well as absorb odors and harmful chemicals
  • User a water clarifier: it wraps dirt particles which makes it easier to filter them out.
  • Maintain regular cleaning and partial water change

Following is a video of more maintenance ideas

More on Fish Tanks & Aquariums


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