How To Clean Algae From Aquarium Rocks | Aquascape Addiction

How To Clean Algae From Aquarium Rocks

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A simple step by step guide on how to clean algae from aquarium rocks the easy and effective way, we also look at the problems algae can cause in aquariums and preventing blooms.

How To Clean Algae From Aquarium Rocks

Algae might be a naturally growing plant or sorts, but that does not mean that you want it in your aquarium. Algae does not always bloom in every aquarium, but at one point or another, chances are that you will see a certain amount of algae in the tank.

It can be caused by various factors, but once it does grow, you might have a bit of a hard time getting rid of it. How to clean algae from aquarium rocks is what we are here to talk about today.

We will also go over some algae prevention tips as well but lets first look at what problems algae can cause to your tank.

Problems Caused By Algae In Aquarium

There are a few things that you do need to beware of when it comes to algae and your aquarium. Now, it is not like it is the worst thing in the world for your fish, but it definitely is not beneficial either.

What are some of the main problems caused by an algae bloom in your fish tank?

Lack Of Oxygen

One of the biggest problems caused by algae blooms is that they eat up a ton of oxygen in the tank. Your fish and plants both need oxygen to survive in one way or another.

Too much algae can cause a significant decrease in water aeration and oxygenation, which is not good for plants or fish.

Lack Of Nutrients

This is especially important when it comes to your aquarium plants. The more algae is in the water, the more nutrients it sucks out of the water.

This can be a real problem for many plants that require the absorptions of nutrients through the substrate and water column.


This does not happen very often, but there are certain types of algae which can be toxic to fish.

Cloudy Water

One of the first and most obvious drawbacks to having a bunch of algae in the tank is that it makes the water cloudy and it makes everything look really dirty.

The water will be milky and discolored, plus your decorations get covered in it too. It really just does not look nice.

Filter Issues

Lots of algae present in an aquarium can be bad for filters. For one, it can clog the tubing and cause media to be used up way too quick.

At the same time, the filter you have might not be able to keep up with the increased demand that it is faced with due to a big algae bloom.

How To Clean Algae From Aquarium Rocks: Step By Step

Whether it is white, black, green, blue, or red algae, and whether it looks stringy, mossy, or puffy, you need to get rid of it if you see it growing in your aquarium. It may only look like a little bit today, but given the right conditions, you might wake up tomorrow to a fish tank full of it.

If you see it growing on rocks and other decorations, you need to clean it off ASAP, and you need to take the right steps to correct the underlying issue too. Let’s do a step by step guide on how you can effectively clean algae from your aquarium rocks and other decorations in the tank.

How To Get Algae Off Rocks

  1. Remove the decorations from the tank. Make sure to go slowly and remove them one at a time, removing too many at once can cause stress to your fish. Make sure not to shake the decorations in the water or anything like that. You don’t want to knock off any algae and release it directly into the water.

  2. You want to move all live plants to the corner of the tank so that the substrate is exposed. Use an aquarium siphon and gravel vacuum to clean as much debris from the rocky substrate as possible.

  3. Now, take the rocks and other aquarium decorations. Place them in pot of water that has reached boiling temperature and let them soak for about 20 minutes. This should kill off a lot of the algae present on the rocks and decorations.

  4. Get yourself a new toothbrush and scrub the rocks and decorations. There is no need to be really gentle here. Get that toothbrush and get into all of the corners and nooks in your rocks and decorations, removing as much algae as possible.

  5. Take a bucket and create a bleach solution. This solution should be 95% warm water and 5% bleach. Soak the rocks in the bleach mixture for around 5 minutes, using gloves to make sure you don’t burn your hands. Now take the toothbrush and scrub the decorations again.

  6. Make sure to rinse of the decorations thoroughly, first with cool water and then warm water. If there is any bleach on the rocks or decorations when you put them back in the tank, it can cause serious health risks for your plants and fish.

  7. If you are worried about chlorine in the water, you can get a bucket of water, use dechlorinator with it, and soak the rocks in the dechlorinated water. Now they should be ready to be put back into the tank.

  8. Put the rocks and decorations back into the tank.

Causes Of Algae Blooms – And The Solutions

Before we get into cleaning algae off of aquarium rocks and how to get rid of it within the tank, it is probably important to know what the underlying causes of the algae bloom is. After all, this stuff does need certain conditions for growth.


Algae love to eat nitrates as well as phosphates. It is one of the main food sources they use to grow. If you have an overstocked tank, chances are that there are a lot of nutrients in the water which will aid algae growth.

Having too many fish will cause ammonia and nitrate spikes, which algae does not mind at all. You need to do everything you can to reduce nitrate levels (the right plants also help). The easiest way to go is with a denitrifying solutions specially built for aquariums.

Inadequate Filtration

If you don’t have a good filter, it can also cause algae blooms to occur. For one, if you have good mechanical filtration, it should filter out a lot of the algae. At the same time, a good biological filtration system should be able to take care of nitrates and other algae food sources.

However, if your filtration unit is not good enough or it is not functioning properly, it won’t remove these nutrients from the water, thus allowing algae to bloom.

Dirty Water

Make sure to clean your fish tank on a regular basis. This means removing dead fish, decaying plants, and old food. All of those things, as they decay, give off nutrients that algae will use to grow.

You need to clean decorations, rocks, plants, the glass itself, and the substrate too. Making sure to engage in regular water changes and regularly cleaning the aquarium will help prevent algae blooms.

Old Lights

We don’t want to get too deep into the science of it here, but aquarium lights tend to change the spectrum of light they release as they age. It is shown that older aquarium lights tend to favor algae growth, especially the really strong ones.

The best way to go about it is to replace aquarium lights every 6 to 8 months. Different lights have different lifetimes, so make sure to do some research on the specific lights you have.


Heat is not the sole cause of algae growth, but when combined with some of the above aspects, a really warm aquarium is definitely a good home for algae. Make sure that the water is warm enough for your plants and fish, but don’t keep it at an excessively warm temperature either.

Commonly Asked Questions

Will boiling rocks kill algae?

If you have algae on rocks in your aquarium, you do want to get rid of it as fast as possible. Now, some people wonder whether or not boiling rocks is enough to kill algae.

The answer here is that no, boiling your rocks will not kill the algae. It may sound weird that the high temperature does not kill the algae, but it may actually worsen the situation.

Boiling rocks with algae may actually cause the algae to burst, and then release some pretty serious toxins into the water.

How do you remove brown algae from rocks?

Yes, cleaning aquarium rocks is something you will have to do regularly in order to remove algae, physical debris, and a number of other contaminants too.

The easiest way to remove algae, such as brown algae, from aquarium rocks is to first scrub them down with a brush to remove as much of it as you can by hand.

Next, you want to create a solution of around 90% water and 10% bleach (brown algae is tough so you will want a good deal of bleach).

Next, soak the rocks in this solution for about half and hour, then scrub them down again with your brush, and finally rinse them off well.

Remember to rinse them off well. If you get bleach into your fish tank, you will have way worse issues than algae.

Can you use bleach to clean aquarium rocks?

Yes, you can use bleach to clean aquarium rocks, and when it comes to rock algae, is actually the most effective way of getting rid of it.

Always be sure to make a diluted solution of no more than 10% bleach and 90% water, and always be sure to rinse off the rocks thoroughly afterwards.

Once again, you do not want to get any bleach residue in your aquarium.

How do you clean new aquarium rocks?

If you feel the need to do so, which you probably should, as new aquarium rocks can be quite dirty, simply boil the rocks first, for about 20 minutes, just to remove all sorts of bacteria and parasites.

Follow that up with a bleach bath, as discussed above, as this will remove remaining contaminants.

Finally, as always, be sure to rinse the rocks thoroughly so you don’t get any bleach or anything else of the sort into the fish tank.


Cleaning algae off of aquarium rocks is really not that hard, but it does take some time and effort. The best way to make sure that you don’t have algae in your aquarium is to take care of the underlying causes right from the get go.

However, if you do find that there is a lot of algae in your aquarium, the above tips are all good things to keep in mind.