How often to Change Water in Fish Tanks? (Get the Proper Guidelines)

How often to Change Water in Fish Tank

Changing the water in a fish tank can be a tricky task. It’s essential to know how often to change water in fish tanks and what types of changes your fish prefer. The amount of time that should elapse before changing the water varies, depending on whether or not it is filtered and what type of filter is used, as well as how many fish are present in the tank and their size. 

For instance, if there are more than 50 gallons of water in a tank with no filter, then it will need to be changed every 2-3 days. However, if there is an efficient filter system with less than 10 gallons of water for one small betta fish, then you only have to change this once per month!

However, those are rough estimations; most fishkeepers do change the water at specific intervals. Some change monthly; some do weekly, and even daily. Who’s right? What regime should you follow? 

Luckily, there are ways to identify accurately how often to change the water in a fish tank. In the below section, I’ll let you know.

  • How often should you change aquarium water?
  • How much water should you change?
  • How often to change the water in a fish tank without a filter?

Why Should You Change The Water In Your Aquarium? 

Fish are cute and cuddly, but they really shouldn’t be in aquariums because their waste pollutes water. In nature, fish are not habituated to living in their own waste. But, the only way to get away with keeping them in aquariums is by using a biological filter to break down their waste products or changing aquarium’s water regularly. 

Without using biological filtration or regular changes in the aquaria’s water content, these precious creatures would die from being poisoned by their own bodily fluids! So let’s know why changing water is so crucial. 

Prevent Detritus Build-Up & Waste Accumulation

When you feed your fish, they poop! Meanwhile, what goes in with their little mouths comes out as urine or feces. Moreover, uneaten food particle sinks to the bottom and decay, which also adds up to the problem of poor water quality. 

The accumulation of waste products in an aquarium is a never-ending cycle. Eventually, these wastes accumulate both as solid debris on the bottom of your tank and dissolved chemicals such as nitrate or phosphate that can cause problems for fish living there if it’s not monitored properly. 

Once you cycle your fish tank initially, beneficial bacteria colonies grow in filters, substrates, and literally all over the aquarium space. They convert toxic ammonia excreted by fish into nitrite (also harmful) then into nitrate (less toxic). 

Nitrate constantly builds up in your aquarium ( a byproduct of biological filtration). The higher your nitrate levels, the less likely it is that you’ll have a healthy and productive tank. The reason is that elevated nitrates hinder growth in young fish and reproduction in adult ones. 

You need to change the water also to lower phosphate levels, remove tannins and staining, and maintain optimum pH and KH. High Nitrates and phosphates are bad for fish. They cause chronic stress, which makes them more susceptible to disease, as well as promotes the overgrowth of algae in the water supply.

But if you don’t change the water often enough, then over time, your nitrate level will likely rise, pH and KH dip too low – which can ultimately lead to Old Tank Syndrome. A biologically effective filter system stops working when the pH level drops so low, and fish are killed off within hours or days after being added to this old tank environment. 

Why Should You Change Water Regularly

Replenishing Minerals & Trace Elements

Reducing waste accumulation is not the only reason for a water change, but it’s worth noting that there are other reasons too. For example, you shouldn’t let your fish suffer from a lack of minerals in their tank environment!

You know that fish need vitamins and minerals to stay healthy, right? Well, new water is just as crucial for them. So if you want your pet fish to be strong in vigor, then make sure they’re getting their appropriate dose of trace elements by replenishing them at specific intervals!

Over time trace elements and minerals are used up or filtered out. Trace elements and minerals are crucial for the stability of water chemistry and for your fish. While these important nutrients also help maintain the pH level, they also supply vital functions for the well-being of the aquatic critters in an aquarium environment. 

How Often To Change Water In Fish Tank? 

How often should you change the aquarium water? Every tank is different, so it’s important to know and understand your specific bio-load. This will allow for a more individualized schedule on the water changes!

It’s evident that an aquarium containing a large number of fish will have more bioload compared to a sparingly stocked fish tank. To determine the water change frequency, you need to figure out how much waste your fish produces. You can do it by testing the aquarium water for nitrates.

Your target is to keep the nitrate level below 40 ppm at any given time. Suppose you have an aquarium that generates 5 ppm of nitrates every week. So, it takes eight weeks to reach the threshold limit. 

How often to change water in aquarium

If the nitrates level reaches 40 ppm and you change 25% of water, you reduce nitrates by 25%. Meaning after a water change, nitrates will be 30 ppm. After two weeks, nitrates will climb back to 40 ppm. So, with the current trend, changing 25% of the water every two weeks will keep the nitrates level below 40 ppm. 

However, if anything changes, like if you overfeed than usual or add more fish, you should look for the rate of nitrates change and adjust your water change frequency accordingly. 

Tips: Sometimes tap water contains some nitrates (usually below 10 ppm); test the tap water too before adding it to the aquarium because it can hamper the calculations. If the tap water has nitrates, use RO water or rainwater, which is purified and free of nitrates. 

Topping Off Vs. Water Change

The water level in the aquarium drops gradually due to evaporation. So, you may think that the addition of the lost water is the same as the water change. However, merely adding water is not enough to remove the wastes from your tank, so don’t skimp on the changes! 

Because by adding water, you are just diluting the wastes but not removing them. If you don’t remove debris through a water change, waste will continue to climb up and eventually affect the fish. 

A reduced water level is also a good indication that it’s time for a water change. When you see the water level has dropped, go ahead and use a gravel vacuum to clean out the substates and remove a bit more water. Then add fresh dechlorinated water (or distilled if possible) until it’s back at an acceptable height for proper fish health and happiness!

Tips: When it comes time for your fish tank to be refilled, make sure you use a clean and safe water source. Age the water one day, and make sure the temperature and pH of the water are close to the ideal range for your fish. 

How Often To Change The Water In A Fish Tank Without A Filter

Nitrates will climb up fast in fish tanks without filters because there are no ways to remove wastes out of the aquarium. You can also check the nitrate increase rates and determine the water change frequency. However, as a rule of thumb, you should change 10-15% of the water daily.

A daily water change will not only remove detrimental chemicals that can decrease water quality but also help reduce debris like uneaten fish food. However, if you do leave it behind, this too could contribute to an adverse effect on the aquarium environment. 

How Much Water To Change At A Time? 

You already know that the frequency of water changes for an aquarium depends on the aquarium size and number of fish. In other words, it depends on the rate of waste accumulation. Usually, heavily stocked smaller tanks require more frequent maintenance than larger ones with less fish density. 

Water changes should be an important part of your schedule tank maintenance. You should set the frequency based on the rate of waste generation in your aquarium. However, I’ll also tell you the general rules of changing water that many aquarists follow. 

It’s essential to change the water in your tank at least once every two weeks. However, ideally, you should be changing a portion of it weekly! The best way to keep your tank fresh is by changing 10-15% each week. But, if you can’t do that every week, change 20-25% bi-weekly. 

If you have a heavily stocked aquarium, bump that up all the way to 25% weekly. For light fish populations (like me), two to four weeks should be long enough before it needs another change over again!

Aquarium Types Frequency & Change Amount
Average Aquarium 10-15%, Weekly or 20-25%, Bi-Weekly
Heavily Stocked 20-25%, Weekly
Lightly Stocked 10-15%, Bi-weekly

Limit the water change to a maximum of 30% of the total volume at a time. The goal of fishkeepers is to keep their aquatic friends happy and healthy. With that in mind, drastic water changes can be very stressful for them.

So it’s crucial not only to recognize how much work goes into doing large-scale changes but also to think about whether or not these actions are necessary at all.

Tips: When performing water changes, make sure to use an aquarium gravel vacuum and bury the head in the substrate. This ensures that any toxins or accumulated debris are also removed along with the water!

Tips To Decrease The Water Change Frequency

You may feel it’s overwhelming to change the water every week, and probably you’re finding ways to reduce the frequency. Below I’ll share some tips which you can apply to decrease the water change frequency. 

Tips To Decrease The Water Change Frequency
  • Buy a quality filter because, without a filter, you have no control over the waste. Therefore, a quality aquarium filter is a must-have if you want to avoid water change very frequently. 
  • Plants take nitrates as the nutrients; therefore, adding live plants those are good at reducing nitrate will help to some extent to keep the nitrate levels low. But please don’t get me wrong, live plants will not cancel out the requirement of water change. It can only be a great addition to reducing the change frequency. 

How To Do A Water Change? 

First, mark the water level in the fish tank to the extent you want to remove it. After that, to do a water change, you will need: 

  • A siphon tube and bucket to start with-The siphon should be started by hand, not sucked for hygiene reasons! Place one end of the tube in the tank and the other end in the bucket; start the siphon, and you are on the go! Keep close eyes on the water level, and no small fish are sucked up in the tube during the process.
  • Aged water – Throw out the dirty water to the sink, or use it for other purposes like watering the garden plants (as plants may suck nutrients from the fish waste). Refill the tank with previously dechlorinated aged water. 

Water Change With Gravel Clean

Get your hands on some gravel vacuums because cleaning your gravel (substrate) while also conducting a water change is the best way to ensure that you have a clean aquarium! 

Uneaten food and fish poo gather up in the substrate and can raise the nitrates level. Therefore, it’s essential to remove these things from time to time.

The size of the gravel cleaner you choose should depend on how big your tank is. If it’s too small, then it will take forever to get rid of all that water. 

On the other hand, too large can make siphoning tough because they may not fit under some tank’s lids, have issues starting up, or they may also empty the tank very fast. Check the review & buying guide for the best gravel vacuum cleaner for your tank size. 

Are There Any Other Ways To Change Water?

Bailing water out can be done with a jug for small tanks. On the contrary, you can use a bucket for large tanks, although it’s a hard physical job. 

If you don’t want to hurt your back, just pump water from the tank. Use an aquarium powerhead or a pump with a hose to remove the water from the tank. 

Wrapping Up

Fish tanks are like small aquatic ecosystems, and maintaining them can be a challenge for even the most seasoned aquarist. Achieving healthy fish growth in your tank starts with ensuring it has all of its necessary nutrients–which means giving those poor dears some love by water-changing often! 

Freshwater is crucial for keeping your fish healthy and happy. You should change the water regularly to remove unwanted substances that could harm them, such as nitrates and phosphates, tannins, and staining from organic matter. 

Fish of specific breeds prefer certain pH levels or KH amounts, so if you’re not careful about matching up, that will hamper their reproductive system. 

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