How Often Should I Change My Guppies’ Water?

You should change about 10% of your guppies’ aquarium water every week to maintain a clean and healthy environment. 

Why Change Your Guppies Water

Changing a portion of your guppies’ water helps in several ways.

Remove Unwanted Food 

As you feed your guppies, a portion of the food isn’t eaten and drops to the bottom of the tank. This food will eventually be eaten by bacteria which will produce waste.

The most toxic of this is ammonia, but it will be converted to nitrates and nitrates as well. If your tank has high levels of any of these harmful compounds, it will harm your fish.

Remove Fish Excretion

Similarly, the food that your fish does eat is digested and excreted as waste. The same thing happens to fish waste as with uneaten food. It is broken down by bacteria into ammonia, then nitrites and ultimately nitrates.

Close up shot of orange, black, and silver guppy

Dangers of High Ammonia, Nitrites and Nitrates

In nature, fish have much more space than they do in an aquarium. Most fish keepers use the rule of thumb of 1 inch of fish to 1 gallon of water.

Could you imagine how crowded a pond or river would be if nature used this same rule? The result is that these chemicals are highly diluted in nature.

As ammonia is produced, bacteria converts them to nitrites, then a different type of bacteria converts nitrites to nitrates.

These are all highly toxic chemicals to guppies and other fish. Too much of any of them will result in stress, illness, disease, and eventually death.

In nature, most or all of these chemicals are absorbed by plants or algae. Just like nitrogen based fertilizers we use in our garden, plants love nitrites and nitrates.

In our aquariums, it’s very difficult to provide enough plants to remove these chemicals naturally. So as a result we need to change our water to remove them ourselves

How Frequently Should I Change My Guppies’ Water

As a general rule of thumb, you should replace 10% of your aquarium water once a week, though there are a few variables that could increase or decrease this.

You should always test your water before and after a water change. You’ll want to test ammonia, nitrite, and nitrates. Be sure they are all in the safe range after the water change.

Variable that Can Impact Size and Frequency of Water Changes

Stocking Level of your Tank

If you’ve got 10 guppies in a 10 gallon tank, you’re going to need to change more water more frequently than if you had 3 guppies in the same 10 gallon tank. More fish will produce more waste. To remove more waste, you’ll need to remove more water.

We prefer doing larger water changes rather than more frequent water changes. But you’ll need to find what works best for you.

Live Plants

Live plants can and will absorb the nitrogen found in nitrites and nitrates. While it’s unlikely that you’ll have enough live plants to absorb everything, it’s possible.

Even if plants don’t absorb all nitrogens, they will certainly absorb some. The only way to know for sure how much water you need to change is to test your water.

How To Do a Water Change

Required Supplies:

  • Bucket
  • Vacuum/Siphon
  • Towel
  • Water
  • Water Conditioner

Step 1: Test Your Water

You want to get a baseline to see what your water parameters are. You should test your tank’s ammonia, nitrite, nitrate, and pH.

I personally like to compare these to a water test done after the water change to be sure I’ve replaced enough water.

This will also raise any red flags before you start the whole process. Your ammonia and nitrites should be zero before the water change. But if for some reason they aren’t, you’ll want to do a larger water change than you ordinarily would.

Step 2: Get Everything Set Up

Get your bucket in a good spot to receive the siphon. You don’t want to have water flowing only to find that your bucket is too far away. This is a recipe for a mess.

Be sure your siphon is long enough to reach all the way into your bucket. You might want to bring in a chair or small table to raise up your bucket to be closer to your tank.

And finally, be sure you have your towel ready. I tend to just throw it over my shoulder so it’s always with me.

Regardless of the hundreds of water changes I’ve made in my life, I always find a way to splash a bit, have some drips get on the floor, or end up with a little water running down the front of the tank.

Step 3: Start the Siphon

Some aquarium vacuums have a nice easy way to start the siphon.

Some have a little squeeze pouch. Some have a valve that will let you pump your vacuum up and down to get started.

If you don’t have either of these, you can start the siphon the old fashion way – with your mouth.

Just suck a little on the end of the tube to get the water moving, then take your mouth off before the water hits your mouth.

If a little water ends up getting in your mouth, it won’t hurt you, but definitely don’t swallow.

You’ll want to remove about 10% of your tanks water as a good starting point.

Step 4: Stop the Siphon

It’s easy enough to stop the siphon – just pull it out of the water.

Be sure to pull it out of the water before your bucket is full. There will be some water that still flows into the bucket after you remove it from your tank. That’s from the water that’s still in the tubing that will need to drain out.

Be sure to leave the mouth of the siphon over the aquarium to let any water remaining in the tube drain out.

Step 5: Dispose of the Old Water

You’ll now have to dump your old water. There’s nothing wrong with just dumping it down the drain.

But I really like to water my plants (or garden if the season is right) with my old aquarium water.

The nitrogen in your water is effectively the same nitrogen that’s found in plant fertilizer.

Be careful with this step. The bucket is heavy and likely close to full. Its very easy for the water to slosh around and splash out.

My best tip is to take it slow. No need to rush while you’re carrying 20+ lbs of water in a bucket across your house.

Step 6: Pour in New Water

Now that you’ve got an empty bucket, you’ll want to start filling it with tap water. Try your best to match the temperature of your tank water. It doesn’t need to be perfect, but it should be close (within 5-10 degrees F).

While the bucket is filling, you’ll need to apply water conditioner. This will neutralize chlorine, chlorides, and other heavy metals from your water. These chemicals are toxic to your fish and will cause stress at best and death at worse.

Again with this step, take it slowly lugging your water filled bucket across your house.

You can either dump the water straight from the bucket into the tank or you can siphon from the bucket if you can get the bucket high enough.

Step 7: Test your Water

Now that you’ve replaced your water, you’ll want to test it again. Just like the first test, you will want to test ammonia, nitrites, nitrates, and pH. If these are in the safe range, you’re good to go!