Green Aquarium Water: Get Rid Of It & Prevent It

Clownfish and Clear Water

Clownfish and Clear Water

Has your aquarium water ever turned green?

We’re going to tell you about the things that can cause green water and the things that can be done to prevent it. We will also suggest 4 types of filter media that can help.

If you are experiencing green water, you must first know what is causing it. Green water is pretty much always caused by an algae bloom. You have algae in your tank.

How can we get rid of the aquarium algae? Let’s first look at why it might have happened, and the answer may present itself.

Algae needs a couple things to survive. Nutrients such as nitrates and phosphates – and sunlight. It’s a plant, so it needs to feed.

Cure: Eliminate All Light For 2-3 Days

It is often said that completely eliminating light from an aquarium for a couple of days will cure an algae bloom. In my experience, it is true. Turn off the aquarium lighting and even consider draping something over the aquarium for periods of time if needed. I’ve had a situation where a small freshwater aquarium had a quick green water problem pop up. After scratching my head for a day I tried this and it worked.

Of course, if you don’t check your water parameters and get those under control your problem could come back quickly once you reintroduce light.

Cure: Use a Diatomic Filter

A diatomic filter is able to pull out the small particles that are clouding up the water. This is a process that is also known as water polishing. There are different hardware filter options out there that are designed for diatomic filtration. This type of filtration is also used in public swimming pools to keep the water clear.

Prevention/Cure: Eliminate Any Direct Sunlight

Sunlight can contribute to algae growth as well if you have a situation where your aquarium receives direct sunlight at any point during the day.

I have my 75 gallon aquarium in a room that does not have a window, but it receives a sliver of light during some of the summer months, through the doorway in the room.

That sliver of light is enough to cause a strip of algae growth just where the sunlight runs through a single corner of the tank. Overall though, the tank doesn’t have algae problems since I mostly have nitrates and phosphates under control. But I always get a small reminder of how powerful sunlight can be to spur algae growth.

Prevention/Cure: Controlling Nitrates & Phosphates

If you want to keep nitrates and phosphates under control, it is best to have good water maintenance practices in place. Do consistent water testing. You can also implement some different types of filter media to help control certain water parameters.

First of all, keep the aquarium maintained well. Do consistent water changes with reverse osmosis water. Remove detritus from the aquarium. Clean and maintain your aquarium filtration systems consistently. If you have let one of these items go without care for a while, and you are experiencing green water, it’s probably best to do a water change and clean your aquarium filtration.

Keep an eye on anything that you actually place into the water of the aquarium. Some types of decor and substrate might leach phosphates into your aquarium water. Do research on anything you want to place into your aquarium to see if it may contribute to phosphate levels in the water.

There is also some different choices in filter media that can aid in lowering nitrate levels and removing phosphates from the aquarium water. Read on to learn more about them.

I don’t like to look at filter media as a single magic bullet for aquarium water quality. I like to use it to reinforce great water quality – while having good water quality maintenance practices in place.

Prevention: Don’t Overfeed Fish, Don’t Overcrowd Your Aquarium

Evaluate whether or not there is a waste problem in the aquarium. Are fish being overfed? Is the aquarium overcrowded? These factors can contribute to excess waste and higher nitrate levels.

It’s best to feed fish only as much food that they can eat in about 2 minutes. If your fish can’t eat all the food in that amount of time, you are probably overfeeding. Time it some time, with a stop watch. You might be surprised.

Prevention: Control Water Parameters with Filter Media

We can also look at using filter media. This can cover many different areas and address different water parameters.

There are four different types of media that I like to use to control the nitrates and phosphates in my aquarium. All can be implemented through the use of a reactor and a canister filter in my case. The reactor is a single chamber reactor hanging on the back of the tank, and the canister is an Eheim, which has large trays/compartments in which to place media. The trays seem to be sized almost perfectly for what I place in them.

#1) Chemi-Pure Elite

Chemi-Pure Elite is pretty amazing stuff. It can remove a lot of stuff from your aquarium water like heavy metals, copper, phenol, ammonia, and other nitrogenous waste. It can be used in both freshwater and saltwater aquariums. I use two pouches in my 75 gallon aquarium, in the canister filter, and replace them every six months.

#2) RowaPhos

RowaPhos is designed to specifically remove phosphates and silicates from the water. Those things feed algae. RowaPhos does not leach anything back into the water if it becomes saturated, and it can be used in both freshwater and saltwater aquariums. I use it in my media reactor.

#3) Kent Marine Nitrate Sponge

This can be placed in filter bags and placed in a filter. It takes a few weeks to get going, as it uses a biological process to help keep nitrate levels low in an aquarium. It can be used in both freshwater and saltwater aquariums. I place this in filter bags and put it in my canister filter.

#4) Activated Carbon

This type of filter media is pretty popular and can also be used in freshwater and saltwater aquariums. Activated carbon absorbs organic compounds and can help clear water. In fresh water aquariums, I’ve cleared green water algae blooms overnight by implementing fresh activated carbon. I have not used this myself in my saltwater aquarium for quite some time, however.

These four media options are worth taking a look at if you need to try to get an algae bloom under control. They will attack the source, and will help remove stuff from the water that feeds the annoying green algae bloom that you are experiencing.


I would suggest first to focus on lowering nitrates through a water change, cleaning any filtration and replacing any media that has expired. Sometimes the simple act of a good aquarium cleaning can help get rid of a green water problem pretty quickly.

But, if you fix the problem quickly, don’t get lazy. Keep good aquarium and water quality maintenance practices in place and prevent a bloom from happening again.

About Luke

the owner and caretaker of a 75 gallon aquarium in his home studio. Good times.

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