Last Updated on December 31, 2019 by Aiden Lindow

How To Remove Algae From Pond Rocks

Here you’ll learn exactly how to remove algae from pond rocks, as this can be a major problem if not taken care of correctly.How To Remove Algae From Pond Rocks

Anyone who has owned a pond either currently or in the past can attest to what a joy they are to have on your property or place of business.

That said, certain issues can arise when owning one that you will need to look out for and fix or maintain.

In the following article, we will be going over one of those issues: algae forming on pond rocks.

We will be going over how to treat and prevent this from occurring.

If your waterfall is in the sun at any time during the day, it can, unfortunately, collect algae at the bottom; especially on smooth surfaces such as rocks.

The first thing that should be done is to thoroughly clean the rocks and boulders.

This can be done either with a pressure washer or by hand using a firm brush.


Going the Pressure Washer Route

If you decide to go the route of using a pressure washer, there are two main ways that I have found to do so easily.

The first one is to drain the pond, then use the pressure washer all around the affected area.

This will not only help to remove everything from the rocks but if there is anything sitting in the bottom of the pond, you will be able to see the pond scum here as well and be able to remove it.

If removing the pond scum and algae this way, it may be necessary to use a pond skimmer after you have refilled the pond, as there is sure to be debris and particles of bacteria and algae that will rise to the surface again.

I recommend the Laguna pt495 pond skimmer, I’ve written a complete review if you’re interested.

There is no need to worry, however, as this is a good thing; it not only means that the algae is not sticking to the rocks and stones, but it also indicates that you have successfully removed most of it.

The second method to using a pressure washer is to remove all the stones and rocks from your pond, then lay them out on the lawn and use a pressure washer here.

If you decide to go this route, it should be noted that the careless use of the pressure washer can do some insignificant damage to your grass or lawn, so extra care should be used.

This method is a great way to make sure that all the algae are removed, and that the stones are dry before placing them back into the pond.

This is personally my favorite method for how to remove algae from pond rocks.


Using a Brush to Remove the Algae

While power washing may be the fastest and most effective way to remove algae from your pond, in some cases it just isn’t an option.

If that is the case for you, you can simply drain the pond and then scrub the algae off from the stones and rocks by hand, using a firm brush (it is advised to avoid a wire brush, as this can damage the look and integrity of your rocks).

To do this, you would take each stone out after draining the pond and scrub off all the algae and bacteria.

Note that it is far easier to remove everything when the stones are still wet, so you may want to keep a small amount of water in the pond while you are working on this process.

After they are dry, you can simply replace them into the pond and begin filling with water.


Using a Pond Rock Spot Cleaner

Using a Pond Rock Spot Cleaner

If your pond rocks have not been cleaned in some time, or you are located in a particularly hot and climate region, it may be a good idea to invest in a quality pond rock spot cleaner.

This is great for those hard to reach areas, or if there is a particular trouble region that you can see in your pond.

To use this type of cleaner, you will want to make sure that the pond pump is shut off prior to using it.

Then you simply spray the spot cleaner around your pond rocks and stones, wait the specified amount of time (generally around 20 minutes), then scrub or power vacuum the rocks.

It is important to note, as well, that using this method may cause some debris to float to the top of the pond water, so you will want to use your skimming net to make sure that you have removed all of the algae debris and floating bacteria.

In addition to the spot cleaner, there are other chemicals that can be used in order to either remove the algae or keep it from growing in the first place.

(More detail on cutting down the algae growth below). However, it has been my personal experience that relying on chemicals to do the work for you is not the best course of action, and nothing can compare to some good old fashioned elbow grease.

In order to make sure that your pond is clean and free of algae, we believe that the best course of action is to manually clean the algae off by either using a power washer or scrubbing by hand.


Post-Treatment Filter Cleaning

Post-Treatment Filter Cleaning

Whichever method you choose to use when removing the algae from your pond rocks, it is important to clean or replace the pump filters afterward.

This will not only prevent the algae from building up in the future, but will also help to filter out any remaining bacteria and debris that you may have missed while removing the algae from your pond.

To do so, you will just need to remove the top or bottom of your pond’s filter pump (some models will have the filter towards the top, while some will have them more on the bottom), remove the filter(s), and hose them down with a garden hose.

It is not recommended to use a power washer for this step, as the filter fibers can be delicate in nature, and using a power washer can mess with and corrupt the integrity of these filters.

In the following sections, we will be going over how to prevent algae from building up in your pond, especially on your pond rocks.


Understanding the Ecosystem of Your Pond

Before knowing how to prevent algae from building up in your pond, it is important to understand your pond’s pH balance, as well as the ecosystem of the pond and organisms that work together.

You can purchase a water testing kit, as this will test for pH, ammonia, nitrates, nitrites, and phosphates to ensure you can keep your pond in check all year.

Algae are primitive plants that, via photosynthesis, combine water and carbon dioxide to form sugars for energy and growth.

Algae produce oxygen, a useful by-product, but when sunlight is not available at night, they quickly respire.

This respiration uses the stored sugars and oxygen to form carbon dioxide, which depletes the oxygen in the pond.

Increasing the number of plants that not only oxygenate your pond but also provide shade (effectively ‘starving’ the algae) can help to reduce the number of algae that is produced.


Prevent Algae From Building In Your Pond

Prevent Algae From Building In Your Pond

One of the first things that should be done in making sure that algae does not build up in your pond is to keep it running as much as you can; this will keep the water filtering through the pump.

When you think about ponds that are constantly cycling water vs. those that are still, you may have noticed that still ponds take on more of green color, and tend to have a stagnant odor.

Water treatments can be used in order to maintain the proper pH balance in your pond.

These are great products that will help to reduce the amount of work that you will need to do in order to maintain the proper balance of chemicals in your pond.

It is important to note, however, that these products can also make the pH in your pond too high, so proper balance is key.

Although adding plants and keeping them in the correct balance with the amount of fish that you have in your pond (having fish is not required, and ultimately comes down to personal preference), is the best method; as it is the more ‘natural’ way to go.

That said, most ponds just don’t simply have an adequate amount of room in order to accommodate the number of plants that it would require in order to achieve the optimal pH balance this way, and as a result, some chemicals will need to be used.



Owning and caring for a pond can be one of the most rewarding and peaceful things in life, but there are some times when it can seem to be utterly overwhelming.

We hope that this article not only helped you know a couple of processes that can be used in order to remove algae from the rocks and stones in your pond, but also aid in knowing how to prevent algae from growing in the first place.

The most important thing to keep in mind is that in order to keep algae from growing, it is important to have the right balance of pH and organisms. After that, it’s all about upkeep and enjoying your pond.