How to remove pollutants from your Aquarium


Aquarium knowledge and technology over the years has made it possible to understand how to remove pollutants easily and effective. Below are ways in which you can remove specific pollutants from your aquarium.

Using activated carbon

Despite your efforts to maintain the tank by changing 80% of the water each week, you will still get a buildup of organics.  This is where Activated Carbon or charcoal comes in handy because it is very effective on pollutants. It should however be used for a limited time.

What is activated carbon?

Activated carbon is a water polisher that enhances water clarity by removing pollutants and absorbs organic molecules by capturing small particles in the tank

Which pollutants can Activated carbon remove from the aquarium water?

The following table lists some of the main pollutants that Activated carbon helps to remove from your aquarium

Absorption Pollutants
High to moderate:Arsenic, Bleach, Chlorine, Colors, Dyes, Hydrogen Peroxide, Insecticides, Monochloramine, Odors (usually larger organic molecules), Detergents, Dissolved Organic Compounds (DOC), Hydrogen Sulfide, Mercury, Soap, Solvent
Fair:Complexed trace elements (due to organic chelator), Iron(as FE 3+), Lead, Vanadium.
Low to no:Alkalinity, Ammonia, Carbon Dioxide, Nitrates, Phosphates, Potassium

NOTE: Activated carbon does not remove most fertilizers in a planted tank except chelated iron, which is a large molecule consisting of iron (Fe) attached to a chelating agent such as an organic acid in Ferrous Gluconate.

How to use Activated carbon

Using phosphate removers

All aquariums have phosphates. That is why aquarium maintenance is such a vital part of keeping a healthy aquarium.

What are phosphates?

Phosphates are the byproducts of the natural breakdown of wastes in the aquarium.

Biological wastes that yield phosphates when broken down:

  • Plant decay
  • Dying algae
  • Fish feces
  • Dead fish

Non-native phosphates in the aquarium are a result of external introduction into the tank through:

  • Fish food
  • Chemicals to buffer the water such as pH and kH buffers
  • Tap water
  • Carbon filters
  • Aquarium salts
  • The tap water

Why is it important to regulate phosphate as a pollutant in the tank?

Phosphate in and of itself does directly harm the fish. It however contributes to the rapid growth of algae in the tank at high levels. They then directly have a negative impact on the fish by contributing to oxygen depletion in the tank.

You should always test the aquarium water to make sure that the ideal phosphate levels remain below the level of 1.0 ppm (mg/L).

How to reduce phosphates in the aquarium

The key to reducing phosphates as pollutants in your aquarium is making sure that you are maintaining the levels.

The following table shows you how you can reduce phosphate levels in the aquarium if the levels are too high.

SolutionHow To
Regular Water Change: Perform regular large water changes to keep phosphate levels optimal (below 1.0 ppm (mg/L)). Additionally, if you use tap water, be sure to test it for phosphates. If your tap water contains phosphate, you will need to use filtered or distilled water with a buffer added into it to use for water changes.
Tank Cleaning: Scrape the inside of the glass. Remove the rocks and other decorations and scrub them well. Let everything settle a bit, then give the substrate a good gravel vacuuming. Wait a few days to give things a chance to stabilize, then clean the filter media to remove trapped algae.
Phosphate Absorber: Phosphate absorbing media is very effective. It can be added to virtually any filter. Remember to rinse everything thoroughly because chemical leave traces in the aquarium.
Phosphate Binder: They will cause the phosphate to precipitate out of solution. Use these with caution, and start at low doses, as adding too much will turn the aquarium water white and can affect the health of the fish. The liquid phosphate binders work in such a way that the phosphate compounds precipitate and become pollutants to the water. They therefore need removal via a mechanical filter.

How to maintain phosphate levels

Once the pollutants have been removed, you should make sure that you maintain the phosphate levels.
The following table shows you ways in which you can maintain the phosphate levels in the aquarium.

SolutionHow To
Change Food: Phosphate is used as a preservative in some if not most flake foods. Research and choose those brands that have lower phosphate levels.
Feed Sparingly:Reduce the frequency and amount of food. Just a small portion of food once a day is sufficient for most adult fish. Make sure to promptly remove any uneaten food from the aquarium.
Water Source: Test your water source. It is not unusual for tap water to contain 1 ppm of phosphate. If the level is high, seek an alternate source for your aquarium water.
Regular Water Changes: Frequent water changes will help keep phosphate levels from rising. Change 10 to 15 fifteen percent weekly, using a low phosphate water source.
Tank Maintenance: Keeping the tank free of debris and algae will help avoid phosphate buildup. Vacuum the bottom frequently to remove uneaten food, plant decay, and fish waste.
Filter Media:Carbon is a good filter media, but it can add phosphate to the water, so choose carefully. Some carbon media, such as those for saltwater aquariums, is formulated specifically to not leach phosphate into the water. Others combine carbon media with phosphate absorbers so you get the best of both.
Filter Cleaning: Regularly cleaning debris from the filter will help reduce the sources of phosphate.
Water Treatments: Buffers that condition the water, alter or stabilize the pH, add trace elements or change the hardness often contain phosphate. Don’t use them if they aren’t absolutely needed. If you must use them, research the product and choose one that contains the least amount of phosphate.
How to Lower Phosphates in a Reef Tank: Mastering Nutrient Control

Using silicate removers

Silicates are the brown “algae” that form on the gravel or glass with a thin, dark brown coating on the aquarium glass. They are basically the inert forms of the chemically resistant dioxide SiO2 of silicon.  

What are Silicates?

Silicates are the byproduct of chemical reactions that for a resistant dioxide SiO2 of silicon.

Most new aquariums will have silicates or brown/gravel algae. Silicate pollutants are mainly caused by the following:

  • Poor lighting or too little light
  • An excess of silicates in the water
  • Too many nutrients in the water
  • Oxygen deficiency in the water
  • Tap water that is high in silicic acid
  • Substrates that leech silicate into the water

Why is it important to monitor Silicates in the Aquarium water?

Silicates have a have a wide variety of solubility, which ranges from the least soluble Quartz (SiO2) to silicic acid. If left unchecked they will disrupt the water quality, specifically the pH.

Do Silicates (in moderation) have a benefit in the water?

Natural occurring silicates do have some advantages:

  • They are known to sustain organisms such as sponges, mollusks & diatoms which are responsible for the growth of zooplankton
  • Diatoms feed on nutrients that might otherwise fuel the growth of other types of algae. Thereb indirectly helping reduce algae in the tank
  • Zooplankton is consumed by fish and corals, whose health start to improve. In this case silicates play an indirect role

How to remove Silicate pollutants from the water

Silicates do not adhere strongly to the tank surfaces and can easily wiped away.

The following table show you ways to remove the pollutant from the aquarium water

SolutionHow To
Clean surfaces: Clean and wipe off the Aquarium surfaces
Clean Gravel: Vacuum the gravel with a siphon will quickly remove coatings from the substrate.
Add resin: Use silicate absorbing resin in the filter. If the problem is due to high silicates in the water, and the brown algae persist, a special silicate absorbing resin can be used in the filter.
Increase Lighting: Increase the lighting to inhibit regrowth of brown algae. As a new tank matures brown algae is often eliminated naturally by plants and green algae competing for nutrients.
Stock Catfish: Some suckermouth catfish will readily eat brown algae, most notably plecostomus and otocinclus.

Can you prevent a buildup of silicates in the aquarium?

Silicates are tough to prevent. Some of them occur naturally. The only option you have is to reduce any excessive buildup. This will require constant monitoring of the aquarium, especially a new one.

You should also do the following:

  • Use of Reverse Osmosis water in the tank
  • Make regular water changes
  • Clean you Aquarium regularly aquarium
  • Ensure that you have good and ample lighting
How to get rid of Diatoms

Using Nitrate removers

Nitrates pollutants are a natural form of dissolved nitrogen that you find in any aquarium. It normally occurs naturally in the aquarium water.

What are nitrates?

Nitrates are one of the natural byproducts of fish digestive tracts that tend to build up in any tank causing a myriad of issues if the aquarium is then not properly maintained. 

If there are nitrate pollutants in the aquarium water, the fish will likely display the following symptoms:

  • Rapid gill movement, high respiration rates
  • Listlessness, acting dazed
  • Loss of appetite
  • Loss of equilibrium, disorientation
  • Lay on the tank bottom
  • Curl head to tail (advanced stages)

Why is it important to remove nitrate from the aquarium water?

High nitrate levels in the aquarium water results into what is referred to as “nitrate poisoning or “nitrate shockwhich can kill aquarium fish.

What is the difference between Nitrate Poisoning and Nitrate Shock?

They are both forms of nitrate toxicity with different intensities.

Nitrate Poisoning

Nitrate poisoning generally refers to the chronic problem. Nitrate poisoning occurs when fish are exposed to gradually rising nitrate levels over any period of time due to:

  • Lack of regular tank maintenance
  • Overfeeding the fish
  • Overstocking fish in the aquarium

If you do not reduce nitrate level, it will result into fish death.

  • Some fish will be affected by levels as low as 20 mg/L
  • Other fish will show no apparent symptoms until levels have reached several hundred mg/L.
  • Juvenile fish are affected at the lower levels, as are saltwater fish.
Nitrate Shock

Nitrate shock refers to the acute problem of rapid onset.

Nitrate shock occurs when fish are suddenly exposed to a vastly different level of nitrate, up to several hundred mg/L.

Although nitrate shock usually refers to a sudden increase in the level of nitrate, fish can be equally shocked if nitrate levels suddenly drop dramatically.

How to control excessive buildup of nitrates in the aquarium water

SolutionHow To
Regular water Change: Perform regular partial and full water changes to keep nitrate levels optimal (below 40 ppm for freshwater). Additionally, if you use tap water, be sure to test it for nitrates. If your tap water contains nitrates, you should opt for reverse osmosis (RO) water to use filtered or distilled water with a buffer added into it to use for water changes.
Use Water Conditioner: Use a water conditioner to convert the nitrates to nitrogen gas, allowing it to exit through the surface. The water conditioner will also bind the nitrates, rendering them harmless to fish and making it possible for the bacteria in your biological filter to destroy them.
Use a Bio-media filter: Enhance your filter a bio-media that will trap nitrates, removing them from the water. The bio-media uses bacteria to filter the water for nitrate removal.
Plant lucky bamboo and pathos: The roots of these plants draw up nitrates as they pass through your filter, removing them from the aquarium water.
Sulphur nitrate reactors: They are very effective at reducing nitrates levels because they use autotrophic sulfur denitrification to lower the nitrate levels in in the aquarium. These reactors utilize anaerobic bacteria that grow inside the reactor: which consume sulfur and nitrates for food. Sulphur denitrators are a bit costly but require the least amount of maintenance.

Can you prevent a buildup of silicates in the aquarium?

Nitrates are a natural byproduct of processes that occur within the aquarium.

You should however constantly monitor their buildup to make sure they do not cause an imbalance in the aquarium ecosystem.

You should also do the following:

  • Make regular partial and full water changes
  • Make sure that all your filters are clean
  • Don’t overfeed the fish!
  • Clean and vacuum the gravel for any food and dead plants
  • Reduce the number of fish in the tank of create partitions to avoid buildup in waste which contributes to nitrates
How to Lower Nitrites in an Aquarium