How to Do a Water Change

As your fish produce waste, they fuel the nitrogen cycle. At the end of the cycle, nitrates are produced. They slowly rise and can reach levels that are not safe and are unhealthy for your fish. Since there is no way for the nitrates to get out of the tank, you must manually remove it.  This article will teach you how to do a water change to remove the buildup of harmful compounds.

Once a week, you should do a water change. 10% of your water should be removed and replaced with treated water. You should also take this time to clean your substrate as best as possible.

By Nevit Dilmen [ CC-BY-SA-3.0]
By Nevit Dilmen [ CC-BY-SA-3.0]

Why Do You Need To Do a Water Change

You feed your fish, right? Of course you do.

Do your fish excrete waste? Again, of course.

As the waste decays, it turns into ammonia and ammonia is very toxic to fish. There is bacteria that eats ammonia and excretes nitrites. 

And guess what, nitrites are very toxic to your fish as well.

Fortunately, there is bacteria that eats nitrites and excretes nitrates.

There are much less toxic to your fish. But they still are toxic in high quantities.

Your aquarium is a closed system. Food goes in, but there’s not way for anything to get out naturally. This is where you step in and change the water.

Water changes help to keep your water parameters at safe levels. And good water results in happier and healthier fish. And happy and healthy fish are more entertaining to you.

Equipment You’ll Need to Do a Water Change

  • A bucket – 2 gallon is probably appropriate. Keep in mind that water weighs about 8 lbs per gallon so anything bigger than 2 gallons becomes heavy and difficult to handle.
  • A siphon – You can use just tubing, but this requires that you manually start the siphon and it’s very difficult to vacuum the substrate. We recommend a siphon like this – there is a valve in the siphon allowing you to get things started without putting your mouth on anything. You “pump” the large end in the water a few times and water will start flowing. The large mouth of this type siphon allows you to vacuum the base of your tank much easier
  • Water Treatment – The water coming out of your tap has chlorine, chlorine and all sorts of minerals in it. This treatment will remove all the bad stuff and make it safe for your fish
  • A towel or two – You’ll need to put your hand into the water. Also, there’s a chance you’ll spill. It happens to everyone regardless of experience level. Having a towel handy will help you get a head start on cleaning up before it runs all over the floor.

Water Change Steps

Test You Water

We recommend you test your water just before you do a water change. So begin testing you water for pH, ammonia, nitrites and nitrates. While you wait for your results, get out your bucket, siphon and water treater. Review your water test results. If everything is within tolerable ranges (ammonia < 0.25, nitrites < 0.25, nitrates <30), you should remove 10% of the water in your tank. (Note: if your water parameters are not within tolerable ranges, you’ll likely want to replace a larger amount – see below).

The Dry Run (First Water Change Only)

The first time you do a water change, do a “dry run” before starting and make sure that your siphon reaches the bucket. We strongly recommend having a place to set down the bucket – meaning don’t hold the bucket (a 2 gallon bucket filled with water will weigh about 16 lbs). Unless you have your tank up very high off the ground, you’ll likely have no issues just putting the bucket on the floor.

Start the Siphon and Clean the Substrate

Put the end of the siphon into bucket and get the siphon started. Once the water is flowing, slowly move the large end closer to the substrate. As it gets closer, you’ll start to see waste, likely fish poop and excess food, getting sucked into the tube. Move it around the base of the tank and suck up as much waste as you can until you’ve removed 10% of the water.

Stop the Siphon

To stop the siphon, just remove the end from the water. Keep in mind that any water still in the tube will end up in the bucket. So don’t wait until the bucket is nearly full to stop the siphon.

Keep an eye on the water level in your bucket. I’d venture a guess than every experienced fish keeper has had an issue either with getting too caught up in vacuuming and forgetting to keep an eye on the bucket. This will result in overfilling or the end of the siphon in the bucket falling out of the bucket. Either way, it’s a mess and it’s not fun cleaning up.

Refill the Tank

After you dump your water (we recommend watering your plants with it – its natural fertilizer), start to fill the bucket with new water.  Be careful to match the temperature of your aquarium as closely as possible. Add the water treatment as indicated in the directions. Once you get enough water to top off your tank, add it to the tank.

Wipe down any mess that you made (it happens), close the lid, and you’re done.

One thing to note – you’ll likely lose a bit of water to condensation over the week between your water changes. It’s nothing to be alarmed about. Just top off the tank when you are adding water.

Side Note: If you have a planted tank, this is the perfect time to trim your plants and do basic plant maintenance.

Test Your Water Again

Once your tank is filled and the new water if thoroughly and completely mixed with the water already in the aquarium, you’ll want to retest your water. You should see your levels at safe levels. Assuming everything comes back at safe levels (ammonia should be 0, nitrites should be 0, nitrates should be less than 20), you’re good to go.

If Your Water Tests Come Back High

If your water tests come back high, you’ve got an issue.

High Ammonia or Nitrites

If your ammonia or nitrite are high, you likely have an issue with your tanks nitrogen cycle. If this is the case, you should start testing your water daily. If the levels continue to rise, you need to consider daily water changes. You should replace enough water to keep the ammonia and nitrite levels safe while you wait for your nitrogen cycle to establish itself again.

High Nitrates

If your nitrates are high, you should simply replace more than 10%. How much water you replace is going to depend on how high your nitrate levels are. Replace enough water to get your nitrites down to safe levels. If you are consistently seeing high nitrate levels, your tank is likely overstocked and you should consider rehousing some of your fish.