Why is my turtle tank water turning green? (Cause & Fixes)

why is my turtle tank water green header

So you thought you were doing whatever it took to keep your pet turtle’s habitat clean.

But then why has the water in your aquarium turned green instead of staying clear as it is supposed to be?

Not only that, but in my experience you will notice that the tank also gets smelly.

It’s time to take action and get rid of the problem before it gets completely out of control.

The green water in your turtle tank is caused by a form of microscopic green algae, and in this guide, I’ll show you how to fix this problem.

Let’s go.

Why is the water in my turtle tank turning green?

A form of microscopic green algae called phytoplankton constantly hides in the water of any turtle tank.

When phytoplankton colonies are under control, there is no noticeable difference in water color.

That being said, if your aquarium water turns green, it’s probably due to an algae bloom:

Having enough direct light and nutrients in your aquarium water creates favorable conditions for its phytoplankton population to grow. Spores of phytoplankton algae, colored green, begin to multiply very quickly and thus fill the water. This event is known as an algal bloom. The water in your turtle tank then takes on a cloudy green color.

In the case of an algae bloom, changing the water in the tank will not help.

This is because the algae spores will keep multiplying and coming back.

In some cases, water changes can even make the overgrowth worse as one of the possible causes could be the tap water itself.

What did you do to help the green algae spores bloom so quickly?

Green water in the aquarium

by GreenPlasticDino

Two main factors promote the proliferation of algae:

  • Direct sunlight. Algae spores are exceptionally good at capturing sunlight and quickly turning it into energy for themselves. Usually, the heat and UVB lamps that we install on the resting area of ​​our tanks are not responsible for the proliferation. However, what can cause one is direct sunlight from a nearby window;
  • Nutrients in water. Anything that isn’t alive in our turtle tanks will end up serving as food for something else. Nutrients that algae spores can take advantage of include nitrate, nitrite, ammonia, phosphate, etc. Unsuspecting imports or neglected export of these nutrients can lead to their abundance in our turtle aquarium water. A non-visual sign of water that is too rich in nutrients is its foul smell of sewage.

Sometimes our tap water contains too much phosphate and nitrate and we unknowingly import them into our tank through water changes.

When I started my turtle farming journey, I used to meticulously maintain my tanks, but they kept growing algae.

Imagine my surprise when I later discovered that the real culprit behind my problems was my tap water:

In a moment of desperation, I bought a basic aquarium water test kit and tested tap water. It was found to contain nearly 20 ppm (parts per million) nitrate and nearly 2 ppm phosphate.

After further research, I found that both of these can contribute to algae problems.

On the other hand, forgetting or neglecting water changes will also result in nutrient-rich turtle water.

If we don’t change the water often enough, the nitrate it contains will build up.

Leftover turtle food and turtle poop are big contributors to this.

Author’s note: Nitrate is a byproduct of the nitrogen cycle that takes place in a closed ecosystem such as an aquarium. If there are no plants in the water to use this by-product as food, the algae spores will.

How to get rid of a proliferation of green algae in the water?

Theoretically, to completely fix green water in your turtle tank, you should:

  1. Eliminate all green algae spores in the water.
  2. Take preventative measures to keep the spores from coming back.

But how do you completely get rid of something that multiplies by the minute?

Don’t worry, you won’t have to tear down and redo your entire turtle habitat.

There are easier and faster methods than this.

To completely rid your turtle tank of green algae blooms, try one of these methods:

1. Block incoming light into the tank for one week.

One thing you could do is completely black out your turtle tank.

This way you limit the light that reaches the algae spores that could suppress the bloom.

You cover the tank with some sort of cloth or towels and leave it like that for a week.

Blocking direct sunlight that may hit your tank from nearby windows also helps.

This does not mean, however, that you should limit the daily UVB light your tortoise receives. Turtles need daily lounging to maintain long-term health.

For this reason, it’s best to move your turtle to a temporary tank where it can bask and bathe.

Anyway, the problem with this method is that every time I tried it, the algae blooms came back.

Also, I have found that other turtle keepers report the same low success rate when blacking out their tanks.

I don’t think it’s worth the extra effort.

Installing temporary tanks, moving my turtles back and forth and still having a slim chance of clearing green in the water is not a good compromise in my book.

However, there is one method I have found that virtually guarantees success.

The caveat is that it’s not free.

However, the second method is much cheaper and less time consuming than completely blacking out your aquarium or moving it away from the window.

2. Install a small UV water sterilizer for 10 days.

This is the method that has completely eliminated algae blooms from my tanks every time I have tried it, without fail.

What I’m talking about here is having a UV water sterilizer.

An aquarium UV sterilizer consists of the following components:

  • An elongated closed bedroom;
  • Its own water pump, which pushes dirty water around a UV bulb;
  • A bulb that emits ultraviolet light.

Ultraviolet light irradiates the green algae spores that pass through the chamber of the device, and as a result, they mutate.

Mutated algae spores cannot multiply. Eventually, all of the algae spores die and your aquarium water becomes crystal clear again.

The whole process is completely passive and installing the UV sterilizer is a breeze.

Here is a visual example of a UV sterilizer that cleans green water in an aquarium:

clean cloudy green water

Once the algae bloom has been completely eliminated, you can move on to using preventative measures to keep it from coming back.

Also suppose it turns out that your tap water is the problem and you can’t afford to change the water source or filter it first.

In this case, you can periodically run the UV sterilizer as a preventive measure.

Either way, there are a wide variety of UV sterilizers you can get for this purpose.

Make sure you get one that isn’t cheaply built as they don’t last long.

In addition to that, look for UV sterilizers with a very good seal to avoid potential leakage issues.

If you don’t have time to do proper research on this and are ok with ordering online, you can check out a good one on Amazon here. I have chosen a UV sterilizer that meets all the criteria above in the link.

A UV clarifier with a 3 watt bulb can treat any turtle tank under 20 gallons in less than a week. The 9 watt version can do the same in tanks holding no more than 55 gallons of water.

If your tank is larger than that, I recommend checking out my aquarium UV sterilizer reviews. This guide has a section with recommendations based on a tank’s gallon capacity, which might save you some time.

However, if you want to understand UV sterilizers in depth, I recommend reading the entire review guide.

Author’s note: Cleaning green water with a UV sterilizer also works in fish aquariums that suffer from algae blooms. I am very happy to have discovered this method.

How do you keep turtle tank water clear in the first place?

I have a separate article that discusses turtle water and how to keep it deep clean. Along with ways to do this, the guide also contains a sample schedule for proper maintenance of the turtle tank.

To sum up:

  • Get a solid cartridge filter and fill it with what is called dental floss filter media;
  • Using an aquarium siphon, clean away uneaten food and turtle waste that can contribute to green water;
  • Load the tank with floating plants that turtles are not interested in eating;
  • Add nimble little algae eaters such as ghost shrimp to the tank (this is for hair algae, not spores);
  • Change the water in the tank with dechlorinated water;
  • Change or treat the water source ahead of time if it’s already high in nutrients.

While all of this will keep your turtle tank intact, using a UV sterilizer on the side is one of the best ways to keep green water at bay.

Let me know how things went for your turtle habitat in the comments.

Sharing is caring!

Leave a Comment