First and foremost I have to point out; green water is healthy for your fish and can only happen in a healthy aquarium environment.  Green water is unsightly and not desirable in a show tank, so we will show you how to eliminate it.  Unlike white or milky water or brown water which is underlying symptoms of a sick aquarium; solutions for which can be found in our previous articles on “white or milky water” and “brown or brownish water”, green water can only happen in a healthy aquarium environment.


Green Cloudiness is healthy.  Under the conditions of excess light (sunlight, daylight or over-extended artificial light) microscopic life is born.  This life is green in color; suspended in the water this causes the overall appearance of the water to appear green. 

These tiny microscopic plants, known as algae, can settle to become a green slime covering gravel, plants, rocks and cling to the glass of the tank sides.  The algae colonies can appear as green strips on the side of the tank as well.

Most aquarium fish will thrive on some green algae as a supplemental food, unless there is an excessive amount. In fact, algae are an essential food when breeding egg laying aquarium fish.  Do not mistake these simple algae plants, caused by excessive light for other algae-like pests we will discuss in other articles, such as hair algae or blanket weed.

We know green algae infestations are healthy, but in many cases it is very distracting and unattractive to look at.  Excessive algae growth should not be permitted in a decorative aquarium.

  Healthy or not, if the aquarium is not pleasant to look at, you and your family will lose interest.  Also, untreated, green algae can quickly turn to brown algae so its eradication is best practice.

The cure is very simple, for minor green water cases, simply cut down the light in the aquarium.  For severe cases; eliminate all light for a period not to exceed 48 hours.  Remember; the algae can be caused by the aquarium light being left on too long.  However, the external light in the room being too bright for too long a period of time can be the problem as well.  Usually green water is caused by actual sunlight hitting the aquarium through an uncovered window.

 

Tips and tricks to “cure” green water:

 

1. The simple way to eliminate green water is to completely cover the aquarium with a blanket for 24-48 hours, obviously turning the aquarium light off for this period of time as well.  When you remove the blanket, clean the filter and change out 1/3 of the water with fresh aged water to remove dead and dying algae.
2. If the sun is shining into the aquarium, the fix is simple, tape cardboard, tinfoil;, aquariums approved tank backing or simply block the window letting in the sunlight and stop the light from falling on the aquarium itself.
3. Use approved algaecide which is made specifically for aquariums, not the variety used for outdoor ponds.  Use as directed.
4. There is a natural way, introduce a large cloud of Daphnia into the aquarium, a quantity too large for your fish to eat all the available live food, and the Daphnia will simply eat the algae which eliminates the “green water”.  The excess Daphnia will be eaten by the fish over the next few days.
5. Add approved potassium product to the water, about 1 grain by weight to every 20 gallons of fresh water.

 

Ways to prevent Green Water:

 

1. Reduce the amount of time you leave your aquarium light on each day, if you leave it on from when you get up till when you go to sleep, the prolonged lighting period could cause excessive algae growth.  About 8 hours – 12 hours is the maximum amount of time to have the aquarium lights on.
2. Use less intensive lighting unless you have live plants in your aquarium, having compact florescent lighting without the presence of live plants is probably what is causing your problem.
3. Add healthy growing live plants to your aquarium environment.  Healthy growing live plants will compete with the algae for the available carbon dioxide, which they need to grow, and in the process give off oxygen, which retards algae growth.
4. Block all outside sunlight from entering the aquarium directly.
5. Remove the aquarium from an area where ambient intense room light illuminates the aquarium for 18 to 24 hours a day.

 

Should the water turn yellow, however, the process has been carried too far before the filtration system can remove dead and dying algae; an immediate 1/3 water change is in order.  The sudden death of the microscopic green algae, due to lack of light or algaecide causes the microscopic plants to decompose and turn the water yellow.  This means that the water is now fouling and must be changed before it turns to a white water problem. 

To fix “yellow water” use the same procedure as fixing white water, click here for our complete solutions.  Remember yellow and white water are the only water colors to really worry about.  White or yellow water indicates decomposing matter within the aquarium and the associated bacterium feeds on oxygen, which in turn can kill your fish and live aquarium plants. 

Unlike plants and algae which feed on carbon dioxide and produce oxygen, yellow and white water bacterium feed on oxygen and produce carbon dioxide.  Fish need oxygen, so fix this problem right away, 1/3 water change and new filter cartridge should solve this serious aquarium water condition problem quickly.  If necessary repeat procedure every 24 hours until the water is clear.