How To Grow Algae On Rocks – 2 Common Ways That Work

While it is true that algae thrive due to a high level of humidity, these plants can still prosper on rocks should the conditions be optimal. Therefore, learning how to grow algae on rocks might not be as challenging as you may think it is.

In today’s article, let’s have a look at how you can utilize rocks as a breeding ground for algae.

2 Popular Methods To Grow Algae On Rocks

Using a cup

The easiest approach to grow algae on rocks is to submerge them into a cup of water. First off, you will need either a plastic bottle or a glass cup big enough to house several small rocks or pebbles.

Remember, the material used on bottles and cups must be transparent. This way, the light can easily get through to the rocks themselves, thus creating favorable conditions for algae to grow.

Now, once you have already set up the container, proceed to fill it with water. Make sure to prepare the type of water so that it fits the requirements of the algae. For example, spirulina algae can only live in freshwater while microalgae is a big fan of salt water.

After the water is finalized, you will need to put in vital nutrients. These include phosphates, nitrates, and silicates. If you are unsure about the number of chemical substances needed for your cup or bottle, consider fetching the water directly from nearby sources such as ponds or lakes.

Next up, start adding pebbles inside the container and put it somewhere near your light source. Ideally, it should be in direct exposure to sunlight. But if not, placing the bottle or cup under an LED light will suffice.

Now, all you have to do is to wait until algae start growing.

algae in bottles

Using your aquarium

In case you have already had an aquarium and would like to grow algae on the rocks, things will be much easier. Since the water and lighting conditions have stabilized, you merely need to find suitable rocks and place them inside the tank.

Now, you might want to examine the surface of your rocks and see whether they are smooth enough for algae to attach themselves to. Once all the rocks are placed inside the tank, spray a bit of calcium powder on these pebbles.

algae on rock

This substance makes sure to remove any dirt or microorganisms that may threaten your algae’s growth. Should you want to speed up the growth rate, you may invest in specific fertilizers. There are chemical compounds designed for aquatic plants that do not harm other aquatic animals.

Finally, you will need to adjust the lighting conditions so that your algae has enough resources for its photosynthesis procedure.

The brighter the light, the better it is for algae to grow. Hence, feel free to give your algae as much light as it wants for half a day.


How long does it take algae to grow in a tank?

On average, algae will need about 2 weeks to a month to fully establish itself inside your aquarium. However, this time frame might change depending on several factors, including the number of fertilizers you put in, the amount of light exposure, as well as your own will.

If you are stringent about not letting algae grow inside your tank, then it will take much more time trying to achieve a solid form. That said, once let loose, algae may increase uncontrollably.

Is algae good for fish?

Despite common belief regarding how algae is a nuisance inside all aquariums, this type of aquatic plant can be rather useful for both your invertebrates and fish.

First off, algae can be used as a water filter. They help to remove dirt and other impurities in the water through the leaves. Sometimes, algae also absorb toxin build-ups and release oxygen for your fish to inhale.

Secondly, many aquatic animals feed on algae. They consider it to be a nutritious source of food and thus are not hesitant to munch on algae. If you cannot monitor the feeding frequency of your fish all the time, using algae as an alternative protein intake will suffice.

Finally, certain types of algae prove to be a perfect hiding place for small fish and invertebrates. Not all aquatic animals are fond of swimming around and playing with others. Should one need to seek refuge from others, lurking inside algae spots is the best course of action.

What is the most common type of algae and where does it grow?

It is debatable what the most common type of algae is. Still, most people agree that golden-brown algae is the most popular. As it can grow in both saltwater and freshwater environments, golden-brown algae may find its way inside all types of water bodies.

How long does it take for algae to grow on rocks?

Usually, algae take around 2 to 3 days to fully grow on rocks. If you wish to hasten the growth rate, consider putting in more fertilizers and increasing exposure to sunlight.

But still, remember to do things cautiously. If you overdo the preparation, other aquatic animals inside your tank may end up suffering due to the excess nutrients and inappropriate lighting conditions.


Learning how to grow algae on rocks is relatively easy once you understand its mechanism. After all, everything you need boils down to the right environments and fertilizers to support these plants. And in case you find these tips and tricks helpful, make sure to share them with your fellow aquarists!