How to Reduce Phosphates in Reef Tank and Aquarium – 7 Ways

The most notorious problem that I faced in my reef tank is the excessive phosphate level problem. I also get the question from the hobbyists that they also go through the same problem. Removing phosphates from a reef tank was supposed to be havoc for me.

But then, I found some processes like water changing, reducing fish feed, using protein skimmer, using phosphate remover, using refugium and algae scrubber, filter media, and cleaning. I have used all these methods in my reef tank and I found some techniques to lower the phosphate level in my reef tank.

Hence, stay tuned with me and grab the ideas that I use for my reef tank to keep it phosphate-free.

How to Lower Phosphates in Reef Tank

Phosphate Reduction in Reef Tank

1. Water Changes

In the beginning, I will suggest that you change the water of your reef tank. To complete this process, follow the steps carefully-

  • Before you can effectively lower phosphate levels in your tank, you need to know the current levels. Test the water with a reliable phosphate test kit.
  • Change the water regularly. Such a practice can help to reduce phosphate levels in your tank. For better results, aim for a water change of at least 10% every week.
  • After making any changes, monitor the phosphate levels regularly to ensure they are within the acceptable range. This will help you identify any issues before they become a problem.

Here I want to mention a fact. Water changes can help lower phosphate levels in a reef tank, but they may not be sufficient to solve the problem entirely. You may need to follow some more steps along with water changing. Let’s know them.

2. Reduce Feeding

Overfeeding can lead to excess nutrients in the tank, including phosphates. That’s why, I always try to provide reduced feeding to my fish. Look how I feed my reef tank fish.

  • Firstly, I determine the appropriate amount of feed for my fish and other inhabitants. Overfeeding can lead to excess nutrients, including phosphates, in the water.
  • Secondly, I feed my fish in small amounts several times a day, rather than one large feeding. This will help to reduce the amount of uneaten food that can contribute to phosphates in the water.
  • Like me, you can consider feeding your fish a lower-phosphate diet. Many commercial fish foods are high in phosphates, so look for brands that are specified and labeled as low-phosphate tropical fish food.
  • Lastly, I monitor the phosphates in my tank regularly using a reliable phosphate test kit. This will allow you to track changes in the phosphate levels and adjust your feeding accordingly.

Thus, following my steps, you can keep the phosphate level in control in your reef tank.

3. Use a Phosphate Remover

Use a Phosphate Remover

The further solution to your problem can be using the best phosphate remover in your reef tank. In this case, you have to test your phosphate levels to determine the current levels.

Choose a phosphate remover product that is suitable for your reef tank. Some popular brands include PhosGuard, GFO (granular ferric oxide), Brightwell Aquatics, and ROWAphos.

Then, follow the instructions on the product label for dosing the phosphate remover. Usually, you will need to place the remover media in a filter or reactor and allow the water to pass through it.

After that, monitor the phosphate level to determine the effectiveness of the phosphate remover. Adjust the dosage as necessary to maintain the desired levels.

Be sure to replace the phosphate remover media regularly to ensure it continues to be effective. Thus, this process can facilitate your reef tank.

4. Using a Protein Skimmer

Skimming helps to remove organic waste and other particles from the water which can contribute to high phosphate levels. Increase the amount of skimming in the tank to remove more of these substances.

For this purpose, you have to be careful about two facts. The first one is to ensure that your protein skimmer is working properly. Check the skimmer regularly to ensure that it is functioning correctly. Make sure that the airflow is sufficient and that the collection cup is being emptied frequently.

Again, another one is to increase the efficiency of your protein skimmer. There are several ways to increase the efficiency of your protein skimmer. This includes adding a foam fractionator, using a bio pellet reactor, or adding activated carbon to the filtration system. 

These methods can help to remove even more organic waste from the water, reducing the number of phosphates. Thus a protein skimmer will help you to reduce the phosphate level in your reef tank.

5. Refugium and Algae Scrubber

Are you still searching for new ways? Well, let me help you by introducing refugium and algae scrubber. Follow the steps that I mentioned here-

  • Set up a refugium

A refugium is a separate tank or compartment attached to your main tank that contains macroalgae, live rock, and live sand. The purpose of a refugium is to provide a natural filtration system that removes phosphates from the water.

  • Add macroalgae

Macroalgae, such as Chaetomorpha or Caulerpa, can be added to your refugium. These types of algae are known for their ability to absorb excess phosphates.

  • Provide proper lighting

Macroalgae require proper lighting to grow and thrive. LED lights or fluorescent bulbs are a good choice for refugium lighting. The lighting should be on a timer, providing around 12 hours of light per day.

  • Monitor nutrient levels

Regularly test the water in your main tank and refugium phosphates. Adjust the lighting and nutrient intake in your refugium as needed to maintain the appropriate levels.

  • Add an algae scrubber

An algae scrubber is a device that uses light and flows to promote the growth of algae, which in turn removes excess nutrients from the water. Algae scrubbers can be added to your main tank or sump and can be an effective way to reduce phosphate levels.

6. Filter Media

If you ask me to suggest a filter media, then I may suggest to you activated carbon. It is a common filter media used in reef tanks to remove phosphates. It works by adsorbing the phosphates onto its surface, removing them from the water.

7. Cleaning

Along with applying those methods, you should keep your reef tank clean. Otherwise, the phosphate level will increase again. You should regularly clean not only the substrate but also the filter.

Therefore, excess food, fish waste, and debris can accumulate on the substrate, leading to phosphate buildup. Hence, vacuum the substrate regularly to remove any debris.

On the other hand, the filter is responsible for removing waste and excess food from the water. So, make sure to clean or replace the filter media regularly to prevent buildup.

If you can maintain these methods properly, they will help you to reduce phosphates in your reef tank. You can use only one of them. But combining some methods may help you much.

Why Do You Reduce Phosphates in the Reef Tank

You may ask me why I am suggesting you reduce phosphates in your tank. Now let me describe that. Reducing phosphates in a reef tank is important for several reasons. Phosphates are a primary source of nutrients for algae which can quickly take over a reef tank.

Such algae growth may cause a variety of problems, including reduced oxygen levels and decreased water clarity. Algae blooms can also harm corals by shading them from the light they need to survive and grow.

Additionally, high phosphate levels can contribute to the growth of cyanobacteria which can be harmful to fish and other marine life in the tank. Finally, excessive phosphate levels can lead to the formation of calcium phosphate.

As you know, high levels of calcium phosphate can build up on the surfaces of corals and other tank inhabitants, reducing their ability to exchange gasses and nutrients with the surrounding water.

That’s why to prevent these issues, it’s important to maintain low phosphate levels in a reef tank by maintaining different ways.

Signs of High Phosphate in Reef Tank

But how can you understand that your reef tank has a high level of phosphates? After a close observation of 3 years, I can understand now if my reef tank has high phosphates or not. I have listed the signs below that you can match for your purpose.

Algae Growth

Algae thrive on high levels of phosphate. If you notice an excessive amount of algae in your tank, it could be a sign that your phosphate levels are too high.

Poor Coral Growth

Corals need balanced levels of nutrients to grow properly. But, high levels of phosphate can inhibit their growth. Hence, such poor coral growth can also be a sign for you.

Cloudy Water

High phosphate levels can cause your water to become cloudy. It creates a barrier in the aquarium or tank view. Cloudy water makes it difficult to see your fish and other marine life.

Increased Nitrates

Phosphates can be converted into nitrates. As a result, it can build up in your tank and cause further problems.

Reduced Oxygen Levels

High levels of phosphate can reduce the amount of oxygen available in the water. It will harm your marine life and will drastically reduce the number of fish and other inhabitants.

What Causes Phosphates in Reef Tanks

Have you understood yet what causes phosphates in reef tanks? To prohibit the reabsorption of phosphates after cleaning, this part is very important. Have a glance at my points. You may explore more than before. 


Excess food that is not consumed by the fish and invertebrates can break down and release phosphates into the water.

Fish Waste

Fish produce waste that contains phosphates. If not removed by a protein skimmer or other filtration system, it can accumulate in the tank.

Poor Quality or Overused Filtration Media

Over time, filtration media such as filter pads, activated carbon, and phosphate-removing resins can become clogged or exhausted, allowing phosphates to accumulate in the water.

Tap Water

Some municipal water sources contain high levels of phosphates, which can be introduced to the tank during water changes.

Live Rock and Sand

Although live rock and sand can be beneficial to a reef tank, they can also contain trapped detritus and other organic matter that can break down and release phosphates.

Improper Cleaning

If the aquarium is not cleaned properly, leftover food, waste, and other organic matter can break down and release phosphates into the water.

What is a Good Phosphate Level in a Reef Tank

In general, a good phosphate level for a reef tank is considered to be between 0.03-0.08 ppm (parts per million). However, the ideal range may vary depending on the specific needs of the corals and other organisms in the tank as well as the type of filtration and nutrient management system in place.

Let’s know about the ideal phosphate level in different water reservoirs-

Water tankIdeal phosphate measurement 
Reef tankBetween 0.03-0.08 ppm (parts per million).
Saltwater aquarium Less than 0.05 parts per million (ppm) or milligrams per liter (mg/L)
Freshwater aquarium Below 1.0 ppm (parts per million)
Brackish aquarium 0.5 to 1.5 ppm (parts per million)
Planted aquarium 1 to 2 ppm (parts per million)
Nano aquarium0.03 ppm (parts per million)
Coldwater aquarium 0.5 to 1 ppm (parts per million) in

How to Reduce Phosphate in an Aquarium

Besides reef tanks, you may be little knowledge about how to reduce phosphates in an aquarium. Follow the below-mentioned methods for this purpose-

Reduce Feeding 

Overfeeding your fish can lead to excess food particles in the water, which can break down and increase phosphate levels. Make sure you are feeding your fish the appropriate amount and removing any uneaten food.

Use a Phosphate Remover 

There are several products available that can help remove phosphates from the water, such as chemical filter media or phosphate-removing pads. Be sure to follow the instructions carefully and monitor your aquarium’s water parameters to ensure you are not removing too much phosphate.

Use Live Plants

Plants can help absorb excess nutrients, including phosphates, from the water. Consider adding live plants to your aquarium to help reduce phosphate levels naturally.

Conduct Water Changes

Regular water changes can help remove excess nutrients from the water, including phosphates. Aim to change about 10-20% of your aquarium’s water every week.

Check Your Water Source

The water you use for your aquarium may contain high levels of phosphates. Consider using reverse osmosis or distilled water for your aquarium or adding a phosphate-removing filter to your water source.

I have explained this factor shortly here. If you want, I can provide you with a detailed guide about this topic.

How to Test Phosphate Level

To test the present phosphate level of your reef tank, firstly purchase a phosphate test kit from a reputable aquarium supply store. Then, follow the manufacturer’s instructions on how to use the test kit.

Take a sample of the water from your reef tank. The sample should be taken from a few inches below the water surface to get an accurate reading. After that, add the reagents to the water sample according to the instructions on the test kit. The reagents will typically include a phosphate testing solution, a test vial, and a color chart.

Further, shake the test vial to mix the reagents and water sample thoroughly and allow the vial to sit for the recommended amount of time, usually between 5-10 minutes.

After it is finished, compare the color of the water sample to the color chart provided with the test kit. The color chart will indicate the level of phosphate in the water, which is typically measured in parts per million (ppm).

For the safety of your tank, record the test results in a logbook or other record-keeping system. This will help you track changes in phosphate levels over time and adjust your aquarium maintenance accordingly. 


How long does it take to reduce phosphates in a reef tank?

In general, it may take several weeks to several months to see a significant reduction in phosphate levels in your reef tank. The time depends on several factors, such as the initial phosphate level, the size of the tank, and the effectiveness of the methods.

How can I prevent phosphates from building up in my reef tank?

To prevent phosphates from building up in your reef tank, it’s essential to maintain good aquarium hygiene. This includes performing regular water changes, using a protein skimmer, reducing feeding, avoiding overstocking your tank, and using high-quality aquarium equipment. 

Can reverse osmosis (RO) water may reduce phosphates?

Yeah! RO water has little to no dissolved minerals or phosphates. Thus, it can help to reduce phosphate levels in your tank.

Final Words

Remember that, lowering phosphate levels in a reef tank is a gradual process and may take some time. Consistent effort and regular monitoring can help you maintain a healthy environment for your reef inhabitants.

You may have to face a lot of trouble in removing them. But, the ideal phosphate level in a reef tank is mandatory for the perfect growth and development of your aquatic inhabitants. I always suggest that prohibiting phosphate from building up is better than removing phosphates. That’s why to notice your tank carefully and get a beautiful reef tank.

Howard Parker

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