How to get rid of green water in the aquarium

This seems to be a very common question at work. Especially during the fall. So in preparation for the upcoming fall, I'm gathering together some tips to solve this problem. Please contribute to this thread by adding your tips or suggestions. Your tip might save a fish's life or at least help keep the tank clear.

Test your water for; Ammonia, Nitrite, Nitrate, and pH.
This should be the first thing you do when there's any kind of concern with the tank. Don't wait till the concern turns into a problem. Act quickly. Don't have a test kit? Go to any Petco with a water sample in a clean ziplock bag. You'll need more than 1/2 a cup of water for good results. If the associate is testing with quick dip strips, then make sure they test for ammonia first. The 6-in-1 strips have small amounts of ammonia as a reagent chemical and can give false positive results on small volume water samples. So bigger water samples are better for this reason. Once the test are done, ask the associate to write down the results for you. Nothing worse than trying to help someone trouble shoot a problem and they tell me the results were good. Without numbers, a good result is worthless. Because the everyone has a different opinion on what is good. Also, never use a food container that has been used. No matter how well you clean it, the material will have been chemically contaminated and throw off the test results. Ask your store for a free water sample container or just use a new ziplock bag.

If the tank has been set up and continuously running for less than two months, don't worry about anything. The cloudy water is a normal thing and attempts to get rid of it will usually make things worse. Just keep testing the water and don't over feed your fish.

Here are common mistakes made.

Overfeeding-There should be no food leftover after two minutes. Use a timer to check yourself. If you feel that you are not feeding enough, then you're probably feed the correct amount. Feeding fish till they are full during the first two months will lead to ammonia spikes that will kill your fish. Under feeding will rarely kills fish as long as you're feeding only once per day. If you over feed the fish then you'll need to syphon out the excess food each time by doing a small water change.

Overstocking-Only get two small danio fish for the first two months while the tank cycles. These are hardy fish that can tolerate low levels of ammonia. They do t eat much and don't produce much ammonia. Or look up instructions on how to do a "fishless cycle". The fishless cycle is faster and doesn't harm fish. Try it! After the tank has cycled, be sure to follow the rule of one inch of adult fish per gallon. This does not mean "one inch of current size fish per gallon". Only experienced fish keepers should exceed this general rule.

Replacing filters too early-Don't replace your filter till the cycle is done. You should check the filters weekly and rinse them often. Common misconception is that rinsing the filter will wash off the good bacteria. This is not true.

Leaving the lights on too long-12 hours or more is too much light. Only have the tank lit for 8-10 hours max. Special emphasis on the word "max". This does not mean "keep the lights on 8-10 hours daily". Less hours is better and fish don't need the lights on at all. The lights are just so that you can observe them. Unless the tank is located in a pitch black room, you probably don't need to worry about having any lights on at all. Ambient light is plenty of light for the fish to see. They only need enough light to see the food and that's it. If the tank is already green, then just keep the lights off for a week. Don't leave the lights on during the night. Most tanks will receive some ambient light from sunlight entering through windows nearby. Doesn't have to be direct sunlight to cause green water. Indirect sunlight bouncing off the floor or walls is enough to grow algae. Keeping the lights on past dark will increase the photoperiod past the "maximum" recommended 8-10 hours. If you must have the lights on at night, I suggest you get a motion sensor to connect to the lights. This device will keep the lights off when you're not in the room. But I highly suggest getting a lamp timer to regulate how long the lights are allowed to stay on.

Not enough filtration-Only a water test will be able to tell you if you don't have enough filtration for the current stocking level. If there are any signs of ammonia or nitrite after the tank has cycled, then that means the filter can't handle the current amount of livestock or food being fed.

Inadequate water changes-Water changes are a must. How much water to remove and how often are difficult questions to answer. I usually recommend at least a 1/4-1/3 volume water change at least once a month. In my experience, most customers misunderstand this as "once a month water change is all that is needed". Not true. Only a water test can tell you if monthly water changes are sufficient. If the nitrates keep rising each month, then the current water changes are insufficient. You'll need to increase the frequency to twice a month and possibly a larger percent of water removed. I never recommend removing more than 50% of the water at any time, unless you're an expert. But if you're having trouble with green water then you're either a novice or beginner. Don't worry, you'll become an expert with experience and research.

Mistake "water change" with "topping off"-These are two different things. At least once a month I have customers describe their water changes as "adding water each week". If water is not removed from the tank, then it's not a water change. Topping off is when you add water to replace what has evaporated. Adding water during a "top off" does not remove any nitrates and allows this chemical to build up over time. You must first remove water from the tank and then replace it with clean water when performing a water change. Water changes are a must for all tanks. Experts have tried to develop ways around it but none are possible for the average fish keeper. Current attempts are costly, require constant monitoring of water quality, adding costly additives, and using large filtration systems with mixed results. Water from the faucet is cheap and easy.

Chemicals-Don't use chemicals unless you have tried all other options. They are dangerous to you and the fish. Green water is easy to cure if you identify the cause and fix it. Using chemicals to remove green water without solving the cause is a big mistake. Its like using a small band-aid on a severed limb. Many fish owners accidentally kill their fish when using algae removers because they are not aware of how low oxygen levels will be depleted. Many do not understand what is meant by "increased aeration during treatment" on the warning labels. When the chemicals kill off the algae cells floating in the water column, it also removes most of the oxygen and increases the CO2 levels. How much aeration is needed, will depend on how much algae is present and how much chemicals are used. Start with half the recommended dosage and be prepared to do an immediate water change if the fish begin the breath faster. Never use chemicals such as algae removers if you're not able to do an emergency water change. Why continuously use expensive chemicals to solve a problem, when the best solution is easy and free? Just identify what you're doing wrong and fix it.

UV sterilizers-Expensive and should be used as a second to last resort, just before the use of chemicals. Using a UV sterilizer will quickly cure green water problems and they work nearly every time. Just make sure the wattage is powerful enough for your size tank or pond. The bulbs are only good for one year of continuous use. Replacing bulbs are expensive. It costs extra money to run them, and they can cause temperatures to rise due to the hot bulbs used in them. If you're not able to identify the problem that's causing the water to turn green, or simply unable to avoid the cause for special reasons, then try using a UV sterilizer. Average cost is $150-$400 and I would advise not buying the super cheap ones. Cheap units don't work for long, may not be powerful enough even though the package says it is, can leak and cause a fire, or leak and electrocute you and the fish to death(not likely but it has happened).

After taking the above tips and suggestions into consideration, you should be able to solve most green water problems. Key points are; keep ammonia and nitrite levels at zero, nitrate levels need to be kept low or preferably near zero, photoperiod needs to be kept under 10 hours total daily, maintain a good cleaning schedule, and most importantly is to test the water often.

Tried everything and still have green water? Start a new thread and I'll help you solve the problem. For best results please list the following things:

Ammonia=?ppm
Nitrite=?ppm
Nitrate=?ppm
pH=?
Temperature=?degrees F/C
Lights turned on at ?am/pm
Lights turned off at ?am/pm
Water color is (dark green, light green, white, or hazy)?
Are you feeding with algae wafers?
Is the fish food green?
What's chemicals are being added?

Please copy and paste the above list of questions in a new thread. Then replace the question marks(?) with the test result readings. Nearly all algae problems can be solved if accurate test results are provided. Thank you.

Question: Why does the tank turn green during Fall?

Answer: In Fall, most trees lose their leaves and no longer block as much light from reaching your windows as they did during the summer. Also, the sun is lower in the sky and more light will enter through windows than during the summer. Most people are busy during the summer and forget to do water changes. This leads to higher nitrate levels later on in the Fall, which cause algae to grow.