Why Does Aquarium Sand Turns Green? (4 Ways To Prevent It)

Image of aquarium sand with green algae

It’s not normal for aquarium sand to turn green. If you notice your aquarium sand turning green, you should promptly step in and fix it before it causes further damage. So, why does aquarium sand turns green?

Aquarium sand turns green when there is an overgrowth of cyanobacteria algae. These algae multiply very fast if the aquarium is poorly maintained, has excess nutrients, or receives too much light. The cyanobacteria algae attach to the top layers of the sand. This makes the sand look green in color.

Let’s talk about this in more detail now.

Green Aquarium Sand — Most Common Cause

A certain type of algae called cyanobacteria is responsible for turning aquarium sand green.

When it blooms, it floats in the water and attaches to the substrate and tank surfaces. By spreading over various surfaces, it makes the entire tank look green.

Now, every aquarium has some type of natural algae growth. While they may stay under control most of the time, algae growth can blow out of control once in a while.

When it happens, it transforms an appealing tank into a slimy green environment.

You can identify cyanobacteria by their blue-green color and distinct musty and foul odor.

When they appear in a tank, they are a small spot initially. However, they can quickly grow into a large colony that spreads all over the water and tank surfaces.

Algae blooms thrive on oxygen and nutrients in the tank. By depleting these resources, the algae reduce their availability to other aquatic life. This may not harm fish and other aquatic animals. However, it can prove fatal to aquatic plants.

What Causes Green Algae Blooms In Tanks?

Most aquariums will have naturally occurring algae growth. It can even be good as they serve as snacks for some fish.

However, under favorable conditions, algae can grow profusely and result in what is called an algae bloom.

When it happens, these microorganisms can overwhelm the tank. They will make the entire water green and even adhere to the substrate and decorations.

These algae have a slimy appearance and make the tank water smelly. They can also make their way into filter cartridges, water pumps, and mess up the entire tank setup.

Here are the most common reasons for green algae blooms in aquariums:

1. Excessive Lighting

Algae belong to the plant family. Hence, they need sunlight for photosynthesis. When your tank receives plenty of sunlight, it becomes a favorable environment for profuse algae growth.

Tanks kept near sunlit windows are prone to algal blooms. Algae blooms also occur in tanks with strong lights or if you leave the tank light on for long durations.

2. Excess Nutrients

Algae thrive on nitrates and phosphates. Fish food contains these nutrients. So, any uneaten food in the tank will release these nutrients into the water.

Additionally, the natural waste produced by fish will also contain nitrates. In some places, tap water has high phosphate content that encourages algae growth.

Overfeeding aquatic pets, not removing the uneaten food from the tank, and overly fertilizing aquatic plants can lead to water chemistry imbalances. When it happens, algae growth increases and leads to the aquarium sand turning green.

3. Poor Tank Hygiene

Unhygienic water is a breeding ground for algae since it contains excess minerals.

The natural waste produced by aquatic animals contains ammonia and nitrites. In the absence of proper biological filtration, this waste breaks down to release toxins into the water.

You can’t see these toxins since they dissolve in the water. However, they alter the water chemistry and introduce unwanted minerals into the system.

Apart from affecting the health of aquatic pets, these toxins also promote the growth of algae and trigger algae blooms.  If your tank filter is not efficient or can’t handle the bio-load of your aquarium, the tank water will turn dirty.

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How To Prevent Aquarium Sand From Turning Green?

The problem with algae blooms is that they appear suddenly out of nowhere. It’s surprising how everything is fine the day before, and you suddenly wake up to a slimy green tank the following day.

Now, you can change the tank water and clean the filter to fix the problem. However, there is no guarantee that it will not return. So, you should attempt to avoid it rather than fix it after it appears.

Regularly check your tank water and substrate for any green spots. If you come across any green algae, follow these steps to prevent it from growing and spreading.

1. Control the lighting.

If your tank is near a window, it will receive sunlight throughout the day. To prevent algae blooms, move it away from the window or use shades or blinds to block the light.

Also, pay attention to the tank lighting. Avoid using powerful lights unless your aquatic plants need them. You can also install a timer to control the exposure time.

2. Maintain good water hygiene.

Stay on top of water changes to ensure that the water is clean and hygienic. Use a strong filter. Change the filter cartridges and clean the compartments of the filter frequently to ensure it operates efficiently.

Uneaten food and other waste particles can settle into the substrate of the tank. Left untouched, they will degrade and release minerals into the water that promote algae growth.

Get rid of these contaminants by using an aquarium gravel vacuum cleaner regularly.

3. Avoid overfeeding aquatic pets and plants.

Fish food and fertilizers have nutrients that promote algae growth. Avoid overfeeding your aquatic plants and pets to keep the nutrient levels under control.

Remove any uneaten food before it disintegrates and releases nutrients into the water.

You can also use testing kits to track the water chemistry levels and regulate nutrient levels. Check your tap water for nitrate and phosphate content before adding it to the tank.

You can also use RO filters to remove excess salts and reduce algae growth.

4. Grow more plants.

Aquatic plants use the same nutrients that algae thrive on. So, aquatic plants will use up nutrients and not leave enough for algae blooms to occur.

You can also add floating plants to cover the surface and prevent sunlight from entering the water. Without enough sunlight, the occurrence of algae blooms will reduce.

Related Further Reading:

How To Get Rid Of Green Algae From Aquarium Sand?

Your aquarium can still have algae that make your sand and other surfaces green despite your best efforts. Fortunately, you can prevent the problem from escalating and overwhelming the tank.

Here are some of the ways to get rid of algae before it gets out of control.

1. Manually remove the layer of algae.

Green algae often appear as a patch on tank decoration surfaces or in the substrate of the tank. The algae will most likely be on the top layer only.

You can get rid of this layer and prevent it from spreading and growing.

2. Turn the sand over.

Algae usually grow only on the top layer of the substrate. You should be able to wipe it out by cutting off the supply of oxygen and sunlight. Turn the sand over to push the particles into the lower layers.

The algae will perish from the lack of oxygen and light. Hence, this is an effective method to control small amounts of algae.

3. Get some bottom-dwelling fish or algae-eaters.

Algae blooms rarely occur in tanks with fish that dig into the substrate. These fish like to dig and burrow in the sand and turn it over. They also snack on any algae attached to the substrate or rocks.

So, consider keeping bottom-dwelling fish like loaches and catfish to control the algae problem. You can also use aquatic animals like shrimp and snails that feed on algae.

4. Do a complete black-out for three days.

One of the most effective ways to stop the proliferation of algae is to completely cut off the light supply to the tank for a few days.

A complete black-out for three days will starve the algae of sunlight. Since they are tiny microorganisms, they will perish.

Moreover, your plants will not be too affected by this temporary lack of lighting. They will perk up immediately after you restore lighting. However, your algae problem will reduce.

Interesting Further Reading:

5. Use a UV sterilizer or diatom filter.

Ultraviolet sterilizers are specialized aquarium devices for destroying microorganisms.

They are safe for aquatic pets and plants. However, they ruthlessly eliminate tiny parasites and germs. So you can get rid of green algae in your tank by using these devices.

Similarly, diatom filters trap tiny particles, including algae, and remove them from the tank water. You can use either of these devices to get your algae problem under control.

If nothing works and your algae problem doesn’t get better, consider harsh chemical agents as a last resort to tackle the problem.

However, these may harm your aquatic pets and plants as well.  So this is not the best way to handle the algae issue.

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