How to Get Rid of Excess Phosphate in an Aquarium

You can expect to find phosphate in an aquarium because they are the natural by-product of waste breakdown in that ecosystem. The phosphate comes when decaying plant matter, uneaten food, and the fish’s excrement.

The main problem with having a buildup of phosphate in your aquarium is that it promotes the growth of algae resulting in water with little oxygen. Ultimately your fish are starved of oxygen and they die.

How to Lower Phosphate Levels in Your Aquarium

Change the water

Usually, it is recommended to change 25% of the aquarium water in order to maintain the underwater ecosystem balance. However, if you are struggling with high phosphate levels, you may need to consider larger water changes to bring down the phosphate level faster. These water changes need to be frequent to maintain a healthy balance in the water. But you need to find a more permanent solution to the cause of the elevated phosphate level to completely eliminate this problem.

Before you put tap water into the aquarium, test it for phosphates. Some cities have reported the presence of phosphates in tap water.

Use a phosphate absorber

Some chemical filtrants are excellent for attaching and absorbing phosphate. These include aluminum oxide and ferric iron granules, which effectively hold on to the phosphate they absorb from the aquarium. But be careful with ferric iron as it clumps. To use it safely use it in a specialized media reactor.

If that is inconvenient to you consider using aluminum oxide which doesn’t clump. You simply put it in a mesh bag and let it go to work by immersing the bag in the aquarium’s overflow box or the sump.

The sump is a tank attached to the lower end of the aquarium. Water flows from the aquarium to the sump to maintain the correct balance of the aquarium. The water is then pumped back into the aquarium and co the water circulates between the main aquarium and the sump tank.

The overflow box also allows water from the aquarium to overflow out. The water then flows back into the aquarium through a pipe to the sump.

Clean the tank

This involves scraping the glass and removing rocks and decorations as well to clean them effectively. Scrub everything well and then let them settle. Next vacuum the gravel thoroughly to remove the detritus which causes the accumulation of phosphorus in the aquarium.

A few days after this cleaning, it is time to clean the filter. Make sure that you take some days after vacuuming the gravel and cleaning the decorations and rocks before cleaning the filter.

Those days are critical to making sure that the newly cleaned tank stabilizes back to a conducive underwater environment.

Cleaning the filter removes trapped algae that were bloomed because of the presence of excess phosphate in the aquarium water.

How to Control Excess Phosphate in the Aquarium Water

Now that the levels of phosphate have come down, it is critical to ensure that they remain low. The following tips will ensure the phosphate remains in low quantities in your aquarium.

Investigate the water sources

Tap water can contain up to 1ppm of phosphate which can create an imbalance in the conducive of the aquarium ecosystem. If the tap water is the culprit consider using distilled or filtered water for the water changes. Introduce 10 to 15 percent of clean water weekly to keep the phosphate levels balanced. That is frequently enough not to interfere with the ecosystem.

Choose the right filter media:

A carbon filter is excellent for cleaning the aquarium but some options introduce more phosphates to the water. Choose a carbon filter that is developed specifically not to leach phosphates into the water. Alternatively, you can consider a carbon filter that features a phosphate absorber to keep the phosphate levels at a minimum.

Consider using refugium

The refugium is a segment in the aquarium that accommodates aggressive algae outside the main aquarium. That means that the environment in the main aquarium remains undisturbed by oxygen-depleting algae. The refugium becomes a space within the aquarium that helps absorb the waste that could otherwise have polluted the main water.

Change the food

Consider changing what you feed the fish. Many flake foods contain phosphate as a preservative. You may not be able to avoid the phosphate preservative altogether because it is necessary for most brands, but you can choose a food brand or option that has low levels of phosphate.

On the same note about food, ensure that you feed the fish sparingly. Do not dump large amounts of food thinking the fish will eat it throughout the day. Adult fish can consume as little as one pinch of food per day. The remaining uneaten food should be removed from the aquarium immediately.

Maintain a cleaning schedule

Develop a cleaning schedule for the aquarium to keep the growth of algae to a minimum and reduce the sources of phosphates. The buildup of nutrients in an aquarium is very rapid and this can change the environment for the fish in a matter of days. To ensure that you get rid of phosphates and other waste by-products cleaning the aquarium regularly is necessary.

Monitor the water

You need to monitor the water in your aquarium regularly to check the phosphate levels. This by-product is likely to find its way into your aquarium at one point or another. There is no escaping it. But with regular check-ups and water testing, you will be able to catch the issue before it becomes a major problem.


Phosphates can pose a major challenge in your aquarium. But the good news is that it is a problem that can be overcome with the right strategies and approaches. There excellent options of phosphorous test kits for home use on the market. Invest in one of these to use for checking the water in your aquarium. Also, to be on the safe side, ensure that you only use filtered or distilled water for the aquarium.