If you didn’t know, algae are not just the murky disgusting slime we see. They can provide some benefits when grown in a controlled manner in an aquarium.

This article will shed light on how you can grow algae on rocks in a way that would benefit your fish and wouldn’t cause any problem in your tank.


What Are Algae?

Algae are a type of plant species. However, unlike regular plants, they do not have roots, leaves, or stems.

But they do have chlorophyll, and they photosynthesize. Planktonic algae are single-celled microscopic organisms that could either be green, red, or brown.

Planktonic algae happen to be the first link in aquatic food chains. Zooplankton feeds on them, while fish and other larger organisms feed on the former.


Can You Grow Algae On Rocks?

You can grow algae on rocks with two different methods, the bottle and tank method. Both of these work very well, with the tank method being more appropriate if you have fish.

The Bottle Method

You will need a bottle, LED lights, and pebbles.

Step One

Prepare your bottle. You can use a glass or plastic bottle but make sure it is transparent.

Alternatively, you can use a transparent bowl. Make sure it is spotless.


Step Two

The next step is to fill the bottle with water. Different types of algae require different types of water to grow. For example, red and microalgae can thrive in saltwater, while spirulina algae prefer filtered water.

If you don’t know where to get saltwater, you can prepare it yourself by mixing salt and tap water till it’s fully dissolved. The typical salinity required is 3.5%.

Step Three

This step is where nutrients like phosphates, silicates, and nitrates are added in. These nutrients are what the algae need to thrive.

You can buy them as supplements in a fish store.

Step Four

The next step is to add the pebbles. Add them one after the other in a way that they all stay at the bottom of the bottle and are not stacked on top of each other.

After that, cover the bottle and wait for about eight minutes.Glass-bowl-algae

Step Five

This step requires adding in your algae sample. If you don’t know the difference between various types of algae, you shouldn’t pick any random one you find in a lake.

Instead, buy a sample from a shop or order one online.

Step Six

Place the bottle in front of direct sunlight or under LED lighting. The algae must receive enough sunlight to grow— typically about 10-12 hours daily.

After this step is completed, remain patient and watch your algae grow.

The Tank Method

You can also grow algae in an aquarium. You will need river rocks, airstone, aquarium fertilizer, and fishbone powder.

Step One


Place the river rocks in the fish tank side by side. Make sure there’s only one layer in your tank, and the stones are not on top of each other.

Step Two

For now, we will be focusing on the green algae, which is the most desirable type of algae to have in your tank.

Green algae thrive in freshwater, so add about two inches of fresh water. Ensure the chlorine level in your water is not high enough to stunt their growth.

You can reduce the chlorine by filtering the water or by boiling the water for about 15 minutes. You must wait for the water to cool down before moving to the next step.

Step Three

Pour a tablespoon of fishbone powder over the stones. You can substitute it with calcium powder.

Add a small amount of fertilizer into the water, then put in the air stone.

Step Four

After about 10-12 hours, place the tank in front of direct sunlight. You can also use LED lighting but ensure it is bright enough and of the correct wavelength (600-700 nm).

Step Five

As your algae begin to grow, change the water of the tank often and pour in nutrients to make sure they continue growing.

Nutrients like nitrate, which come from fish waste, and phosphates which indirectly come from fish food, can increase growth.

The pace at which the algae will grow on the rocks depends on the nutrients, light source, type of algae, and water parameters.

In most cases, using direct sunlight takes up to 10 days, but with LED lights, it usually takes three or four days.

Benefits of Having Algae In A Pond/Tank


Algae get rid of unwanted pollutants from the water, for example, nitrates.
The presence of algae in your tank can help increase the oxygen level.
Algae serve as a food source for many invertebrates and fish in the tank.
When they are not much in number, algae increase the beauty of the tank by imparting it with various colors.

Common Pitfalls

When growing algae on rocks, one of these problems could arise.

1. The Algae Can Die-Off

A common reason for this is the lack of proper nutrients needed for the algae to flourish. To prevent this, make sure to add enough nutrients to the water.

2. Slow Growth

This is another common problem most people face while growing algae. As we’ve said before, the duration of the growth is dependent on some factors.

The trick is to be patient. However, you can increase the duration of sunlight exposure and add nutrients to fasten the process.

3. Overgrowth

An overgrowth of algae is pretty harmful to your tank. It could lead to a host of problems, as we will see below.

Why Too Much Algae is Bad For a Fish Tank?


It is crucial to control the growth of algae in your fish tank, no matter how beneficial they prove to be. An overabundance of algae can result into:

1. Stunted Growth Of Plants

Sunlight and carbon dioxide are necessary for plants to produce food during photosynthesis and this process leads to them giving off oxygen.

If too many algae are in the tank, they compete with the plants for vital resources such as sunlight.

Without enough sunlight, photosynthesis cannot take place. This ultimately leads to stunted growth in the plants.

2. Lack of Oxygen

During photosynthesis, oxygen is produced, which is absolutely vital for aquatic plants and animals.

However, algae interfere with this process without producing enough oxygen on their own.

The demand for oxygen rises during nighttime when photosynthesis stops. The oxygen level can decrease to a point where the fish in your tank struggle to survive.

3. Dirty Appearance


Having an overload of algae in your tank gives it a disgusting and dirty appearance. The water appears murky, and the whole point of maintaining an aquarium for aesthetics seems futile.

How To Control The Growth of Algae?

It’s straightforward for algae to reproduce since they do it without mating by splitting cells. If they are not properly monitored, they can quickly colonize a tank and render it unfit for other organisms.

1. Limit Sunlight

If the amount of light your tank receives is too high, typically about more than ten hours daily, it increases the chances of unwanted algae spreading all over your tank.

2. Use Them As A Food Source

This is a good way to control algae growth in your tank. There are some fish and other invertebrates that like to feed on them, which can be introduced into your tank.

For example, Turbo snails will happily eat any kind of algae without causing any harm to your tank.

However, be mindful that introducing these algae eaters when you have little of them may lead to them completely vanishing, which could prove harmful.

3. Cut Out Some Nutrients

Phosphates and nitrates are essential to the growth of algae. You have to reduce their levels to stop their overgrowth.

Be mindful that unfiltered or low-quality water usually has a high amount of these nutrients.


There are plenty of reasons to grow algae on rocks. It could be for a fun science project, to add color to your fish tank, or to give the invertebrates in your tank an alternate food source.

Whatever be the reason, the whole process is easy to accomplish and doable if you correctly follow the steps above.

Share to spread love!

Similar Posts