How Often Can You Change Aquarium Water?

Changing the water in the aquarium isn’t optional. It is essential to keep your fish healthy and happy.

If you have a small tank, change 10 to 15 percent of the water every week. If you have a bigger tank, change 20 to 25 percent once every two weeks. The goal is to keep the nitrate levels under 40 ppm for a freshwater tank and about 20 ppm for the others.

This piece will discuss why, when, and how to change the water. Let’s begin.


Why do You Need to Change the Water in Your Aquarium?

Getting a fish tank is great, but you need to take care of their home just like any other pet. And having an aquarium or a fish tank means you need to change the water now and then. This is because fish pollute the water with their wastes. There’s also food that you give the fish that they haven’t eaten.

This will gather at the bottom of the tank and decay. It ultimately reduces the water quality in the fish tank. This is inescapable, and hence the solid debris must be removed every week.

Naturally, fish don’t like to live in a tank with their waste floating around. So, you need a filter that will break down the waste, or you need to change the water regularly.

If you are not going to use biological filtration or change the water, they will be poisoned by their bodily waste and die. So you need to change the water in the aquarium. There are other reasons to do this too. Let’s take a look.

Reset Water Parameters

Water in an aquarium has many parameters like pH level, carbonate hardness, nitrates, etc. These numbers must be checked regularly and maintained at a healthy level to keep the fish alive and healthy.

These values also help you understand how your aquarium is performing. You must check them every week to make sure that none of them are at a toxic level for the well-being of the fish in the tank.

While you’re at it, you must also check the levels of trace elements like calcium, copper, and iron to know whether or not you need to add fertilizer or supplement to the water.

If you have other items like plants in the tank, you must also check on CO2 levels, dissolved oxygen, and redox potential.

Remove Toxins

Water changes are vital to remove toxins from the fish tank. This will keep the debris out of reach for the fish. Using a gravel vacuum is helpful for this reason. It makes the process of changing the water effectively.

Prevent Detritus Build-up & Waste Accumulation

Every aquarium has some level of nitrate build-up, especially if you are using biological filtration. If the levels are too high, the tank will not be healthy for your fish as it affects their growth and reproduction. So, if you neglect to change the water, the levels will reach critical levels, and you will have to deal with Old Tank Syndrome.

The same is true for phosphates because they can lead to chronic stress, making the fish vulnerable to diseases and causing excessive algae growth in the water.

You must also change the water to remove the stains and tannins periodically. The dipping of pH levels is also a problem when the filters don’t work correctly. This can kill the fish in days, if not hours.

The filters will allow for good bacteria to grow across the aquarium, which converts toxic ammonia coming out of the fish into toxic nitrate and eventually into less toxic nitrate. But it would be best if you still got the nitrate out by changing the water and cleaning the tank.

Replenishing Minerals & Trace Elements

Fish need minerals in their water. This keeps them healthy and strong. So, they need a good dose of trace elements periodically. To ensure this happens, you need to maintain the tank’s water chemistry. This way, you can keep the tank’s nutrients intact and maintain the pH level, essential for their vital functions.

How Often Should You Complete a Water Change?

This depends on the type and size of the fish tank you have. The bioload for each tank is different, which means the schedule is determined based on your specific tank and its content.

Now, if an aquarium has a lot of fish, it has more bioload. So, you need to understand the amount of water the fish in the aquarium produce to figure out how often the water must be replaced. This can be done by checking the nitrate content in the water.

Ideally, the nitrates must be less than 40 ppm at all times in a freshwater aquarium. So, if your fish tank creates five ppm every week, you need to change the water before eight weeks when it hits its peak. And if you change about 25 percent of the water, you reduce the nitrate content by a quarter.

But it also means that you will need to get back on the job in two weeks. However, this is still an acceptable practice since the nitrate level is under control. If you end up feeding the fish more than usual or adding fish to the tank, you will need to recheck the nitrate level and adjust the schedule accordingly.

Top It off or Change the Water?

Now you know that you can change all the water or just part of it. It is important to remember that the water in a fish tank is occasionally reduced because of evaporation. So you should add water to make up for what is lost. And you can also use this as a natural reminder to change the water in the tank.

If this is not a minor addition, you can consider this a water change. But it is important to remember that it won’t remove the waste in the aquarium. So, remove the substrates with a gravel vacuum, and don’t be skimpy with the amount of water you add.

It is also important to remember that the water you add will dilute the waste and not get rid of it entirely. This means you must continue changing water and removing debris from the tank so that the fish are healthy.

Now, try to add dechlorinated or distilled water when you are doing this so that the fish are happy and healthy with the right amount of water in the tank.

How Often to Change the Water in a Fish Tank without a Filter

As mentioned before, this will depend on the number of nitrates in the fish tank. But, again, this will happen sooner if you don’t have filters because there is no other way to remove them. If you don’t know how to check the nitrate levels, you should go by the thumb rule of changing about 10 to 15 percent of the tank water daily.

Changing the water every day will help you get rid of the harmful chemicals that will reduce water quality. But it also means that you will be able to remove debris to a certain extent. Remember that a lot of the debris is at the bottom of the tank. So, you might not get it all out with a shallow switching of water.

How Much Water to Change at a Time?

The frequency with which you should change the water depends on the size of the fish tank, the number of fish in it, and the rate at which waste is accumulated. So, smaller, heavily stocked tanks need to be maintained more than big tanks with fewer fish.

Changing the water is an essential part of aquarium maintenance, and the schedule must be made scientifically. First, measure the amount of waste accumulated and adjust the water accordingly. Here are some pointers to help you do just that.

The ideal case scenario is changing some of the water, i.e.10 to 15 percent, every week. But if that is not possible, you must change 20 to 25 percent of the water at least once in two weeks. If your aquarium is heavily stocked, change 25 percent of the water every week.

You don’t have to water more than 30 percent of the total water in one go because a significant change stresses the fish in the aquarium. And the goal here is to keep them happy as well as healthy. So, don’t get over-enthusiastic and think you are helping the fish out.

Tips to Decrease the Water Change Frequency

If you can’t change the water every week, you must look for alternatives to keep the tank clean enough without a water change.

Here are some other ideas.

Use Plants

Adding plants to the fish tank is good because they consume nitrates as nutrients. They will reduce the number of nitrates in the tank and buy you some time. It doesn’t mean that adding more plants will remove the need to change water altogether. They are just meant to give you some legroom in the maintenance schedule.

Don’t Overfeed

Overfeeding the fish in your tank will cause the uneaten food to sink to the bottom of the tank and turn into debris. This will only increase the need to clean the tank more often than you.

Don’t Overstock

You don’t want to keep too many fish in one tank because it will create an imbalance in the tank. It also doesn’t help to add more water to the tank because that does not reduce the amount of debris. Instead, it will just keep the waste floating all over the tank.

The ratio here is not water to fish but tank size to fish. The best way to avoid this is to buy a slightly bigger fish tank in case you might want to add one or two fish in the future.

How to Do a Water Change?

Here is a step-by-step guide on changing the water in a fish tank.

  • Step 1: Mark the water level to ensure you don’t remove more than that.
  • Step 2: Get a siphon tube and a bucket. Place one end of the siphoning line in the tank and the other inside the bucket.
  • Step 3: Start the siphon with your hand and check the water level carefully. Also, make sure none of the smaller fish get sucked into the tube.
  • Step 4: Get rid of the dirty water or use it to water any plants you might have.
  • Step 5: Refill your aquarium with clean water.

Water Change with Gravel Vacuum

Changing the water in a fish tank with a gravel vacuum is a good idea because you can also clean the substrate. The debris from the leftover food and the fish poop gets gathered in the substrates, which raises the tank’s nitrate levels.

It would be best if you got a gravel cleaner based on the size of your tank. If you get one too small, it will take a long time to get rid of all the water in the tank. And if you get one that is too big, it won’t fit under the lids of the tank, and clear out the tank too quickly.

Are There Any Other Ways to Change Water?

You can also use a jug to get the water out of a small tank. And if your tank is large, you can get a bucket to pull the water out. Unfortunately, these are the manual ways of removing the water, and they are not the easiest.

You could also get a pump with a hose or an aquarium powerhead to change the water.

Final Thoughts

How often you can change aquarium water depends on the size of the tank. And you shouldn’t change all the water at the same time. Aim for 10 to 30 percent based on the aquarium’s size.

Jack Dempsey
Follow Me