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How to Change Aquarium Water – All You Need to Know

how to change aquarium water
Written by Simon Michel
Last Update: March 8, 2022

Fish, as most know, are sensitive creatures. For those of us who keep fish it is important that we take good care of their delicate little constitutions and pay attention to the details so we can keep them happy and healthy. One such care-taking task in the realm of aquarium maintenance is quite shrouded in confusion, uncertainty and mystery. That is the task of Aquarium water changes. Doing this too often, not often enough, or the wrong way, can result in sick or dead fish and as such it is vital we understand the when and how of this process. Changing water in fish tanks need not be a complicated affair. So let’s get into it and I’ll give you some tips that have served me well!

How to Change Aquarium Water

1. What You Need

For the changing process, you will need to containers big enough to contain the water in your tank. Ensure at least one of these is squeaky clean and free of any and all chemicals. You will also need an aquarium vacuum. This is more preferable than necessary but it is the best way to get the job done. If you cannot get one, you will need a hosepipe long enough to reach from the tank to the water container. You will also need a water thermometer. This is extremely important.

2. Remove the Old Water

Use your siphon/vacuum to remove the water currently in the tank. Make sure the other end is placed into the container. If you are using simple hose piping, dip on end in the fish tank, suck on the other end of the hose to create a vacuum, and place that end in the container. If you are using the vacuum, run it gently along the gravel bottom of your tank so you can suck up all the gunk between the stones.

Ensure that you have turned off any electrical features such as lights or an aquarium filter. Remove and clean these, leaving them one side.

How much water you siphon out is dependent on what you’re changing the water for. If it’s a normal change, you can drain out between 20 and 45 % of the water. If you are changing due to a serious problem or contamination issue in the water, siphon it all out.

If taking it all out, be sure to scoop up your fish, along with some water from what’s already in the tank into a bag. Tie off the bag but leave some oxygen between the water level and the top of the bag. Place the bag containing the fish in a separate third container that contains some of the water you will be putting into the tank. This will allow the fish to acclimate properly, relieving potential stress.

When the old water is fully or partially removed, also remove the decorations and gravel in your tank. Give them a good wipe-down so as to remove any build-up on them.

If you are changing aquarium water for goldfish or similar species and you have them in a bowl or tank with no filter and pump I suggest you replace all the water every time.

3. Prepare the New Water

Pour the new water you will use into the clean container that is free of detergents and chemicals. Make sure you have tested the water and ensured it has enough minerals and is free of harmful substances or high concentrations of nitrate.

4. Matching Aquarium Water Temperature

Use the thermometer to check the exact temperature of the old water. Add warm or cool water in relevant amounts to the new water until it reads the exact same temperature. This is important as temp changes can severely distress fish.

Use the vacuum or hose pipe in reverse now to suck water from the container of new water into the tank. If you are only replacing a portion of the water and your fish are still in the tank, be careful not to knock any of them with the pipe or while working in the tank.

5. Test Aquarium Water Parameters

Once the new water is in, stick the thermometer back in and ensure the temperature is still the exact same. Slowly adjust if it is not. Test the content of the water too so you can ensure it is well balanced.

6. Replace the Decorations

You can now put back your gravel if you need to remove it for cleaning, along with your other tank decorations. Be careful not to bump any of the fish in the process! The success of an aquarium lover depends on the beauty of the aquarium and the health of the fish living in it. You can get help from these tips for a successful aquarium.

7. Reconnect the Electrics

If you had a filter or lights running in the tank, reconnect them now and turn them back on. Ensure the pump and filter are working correctly.

If you removed your fish, put them in the new water inside the tank while still in the bag. Leave them like this for half an hour. When the half-hour is up, release them into the new water. If the old water was contaminated, ensure none of it gets mixed in with the new water.

And you’re done!

How Often to Change Fish Tank Water

Standard Water Changes

Water change frequency is slightly frustrating to figure out because it differs depending on a number of factors. When trying to figure out how often to change aquarium water, take into account the number of fish living in the tank first. If there are only one or two, there will be less decaying food at the bottom of the tank, less poop, and less nitrate content. This means you are not required to change the water as often as it will take longer for the water to become dirty enough to change. The minerals in the tank will also last longer as there is not much fish using them up. In such cases, changing about 30% of your water every ten days should suffice. Do frequent water tests at the beginning to ensure this is the case and monitor the health of your fish as you do.

If there is a higher population of fish in the tank, there is more decaying food at the bottom, more poop, faster mineral use-up, and higher amounts of nitrate. This then requires more frequent changes. In this case, try changing at least 35% of the water at least once a week. Monitor your water and fish to ensure this is effective.

Emergency Water Changes

If you realize something is wrong with the fish, do a water test immediately. If it shows too much nitrate, not enough minerals, or some kind of contamination or unhelpful substance in it, you need to change all the water immediately. When doing so be sure to clean the tank thoroughly as well. This includes the pump, filter, lights, gravel, and decorations. Do not do them all at once though as you risk wiping out the good bacteria on their surfaces and remove their chances of regeneration. Remember to separate the fish from their tank and put them in bags that rest in the new water so they can acclimate.

One does not need to remove all the water every single time they do standard changes but this is important if doing an emergency change. If you follow this guide, and don’t knock out any of your fish in the process, you should maintain healthy happy fish that enjoy their nice freshwater aquarium!

About the author

Simon Michel

The plight of life sometimes takes you to extremes of nature and guess what, you learn the best lessons in your most difficult times. As a keen sea explorer with several years spent in yachts business, I had damn busy schedules throughout 13 years of my career. I used to free my mind from my mundane days in the sea with extreme fishing expeditions when this became not just a fun activity, but a life saver. You could say, I employed most types of fishing techniques but nothing felt better than fly fishing. That drew my whole attention for a good number of reasons. I mean, it’s an amazing feeling when you are in a light mood with buddies munching snacks and casting the fishing road. I look forward to making the most of my leisure time with this fantastic sport.

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