Planted Discus Tank with Green Water Algae
Photo by Ron Lutz II

Help!! I Have an Algae Problem

originally by Bing Sheng (February 2005) with additions by Evan Yeh (September 2009)

It happens to everyone who keeps an aquarium for any length of time. Your little masterpiece is humming along in a nice balance of chemistry, lighting, livestock until BLAM! Once crystal clear water turns a pea soup green, brown slime covers every square inch of the gravel bottom and staghorn algae is blooming off plants. Okay, maybe its not that bad but when you're in the midst of the invasion, it doesn't seem that far off!

Add More Fast Growing Plants

Adding more fast growing plants is a very effective way to deal with many types of algae problems. In fact often it is more effective to think in terms of increasing the amount of plants and keeping your plants healthy rather than focusing on getting rid of the algae. A tank full of thriving, fast growing plants is much less likely to grow algae than a tank that has few plants, or only slow growing plants. Take a look at our aquatic plants page for a list of fast growing plants.

Adjust Your Lighting

How Long Are Your Lights On?

A very common cause of algae problems especially in low light tanks is having your lights on for too long. Shortening the photo period (the amount of time you leave your lights on) can help you get an upper hand on algae. Putting your lights on a timer can help you pinpoint the ideal photo period to maximize your plant growth without encouraging algae. If you are having an algae problem, slowly scale back your photo period, 30 minutes each week until you reach 6 hours. Then when your algae problem is under control, start lengthening it again, 30 minutes each week until you find your "sweet spot." This will be the point where increasing the light no longer produces increased plant growth. Typically this will be between 8 and 10 hours.

More or Less Light

If you are running a large amount of intense light without CO2, turning off some of your lights may be of benefit. If you have a very weak light that is unable to support sufficient rapid growing plants, you may consider upgrading your light. As a general rule, we recommend running a minimum of 1.5 - 2 watts per gallon to successfully grow plants. You get this number by dividing the total watts of your light by the amount of gallons of your tank. For example if you have a 40 gallon tank with 96 total watts of lighting that would give you 2.4 watts per gallon (96 divided by 40). Plants require direct light of sufficient intensity (typically measured in watts). If you have a very weak light fixture (low watts) you CANNOT make up for the lack of intensity by keeping the light on for longer. Weak lights on for a long time is a recipe for growing algae.

Supplement with CO2

Carbon supplementation improves the overall health of your plants and can keep algae at bay. There are three major ways to add a source of carbon to your tank.

Seachem Flourish Excel

Flourish Excel is a liquid carbon supplement that is a great choice especially for lower light tanks. It is easy to control the dosing and requires no hardware setup. Some people have had success using larger doses of Excel as a spot treatment to kill certain types of algae (black brush algae) that can grow on plants and driftwood. Before doing this, please talk to us as large doses of Excel can kill shrimp and certain plants like Vallisineria.

Yeast Based CO2 Setup

This method of CO2 supplementation involves growing and feeding a culture of yeast in a bottle and directing the CO2 produced by the yeast culture into your tank. We carry a few different setups that are fairly easy to setup and affordable. The advantage of this approach is that it is relatively inexpensive to start up and can produce ample amounts of CO2 for tanks 40 gallons or smaller. The disadvantage is that because you are dealing with a live culture, it can be difficult to control the amount of CO2 produced in your tank.

Pressurized CO2

The most consistent way to add CO2 to your tank is a pressurized CO2 tank with a solenoid valve. This allows you to bubble CO2 into your tank at a constant rate. You can connect the solenoid valve and your lights to the same timer so that the CO2 only bubbles into your tank when your lights are on and your plants are actively using the CO2 for photosynthesis. Although the intial setup costs are significant, this approach produces a very consistent amount of CO2 that you can scale very easily. Also in the long run, this is the cheapest method of CO2 supplementation as refilling the tank is cheaper than feeding a yeast culture or purchasing Excel on an ongoing basis.

Green Water

First off, if your tank is less than a month old - Relax! Many new tanks will go through a green water phase which is really just single celled algae floating around. They are feeding on the overabundance of Ammonia, Nitrites and other nutrients in the water as your tank is completing its cycle. Cycling a tank has always been a part of a raw tank start-up but you can speed it up by adding live nitrifying bacteria culture (ask us about Tetra Safe Start when starting a new tank). Don't worry, as the tank chemistry stabilizes, ammonia, and nitrites will convert to nitrate and will no longer be available to algae. What about the nitrates you ask? Well, that's the beauty of live plants; they will pull nitrate (including ammonia and nitrite directly) as well as phosphate (another cause of algae blooms) right out of the water. Without live plants, the only way to remove nitrates is by regular water changes.

You can avoid a Green Water algae outbreak when starting a tank by initially stocking with ample amounts of fast growing plants.

Algae growing on my tank glass

Yep, it's going to happen. The trick here is to clean your glass often before the algae really attaches to the glass. Use the trusty glass cleaning pad (acrylic tank owners use pads made for your tanks) or the nifty magnet cleaners (one of the "better mouse trap" ideas along with the venturi driven water changers). If you do this as you see it forming, the green haze will come off like a gentle cloud and no longer be a problem. The longer you wait between wipings, the greater chance for the hard "green spot" algae to attach to the glass. You will not believe how hard this stuff will stick--removal will most likely require the use of a scraper cleaning tool. It only takes 30 seconds to wipe the glass with a magnet cleaner so do it every week or as necessary and give yourself a break from "wet arm syndrome".

Algae Growing on Rock, Wood, and Decorations

Heck, you can just take these guys out and give them a good, hard scrubbing under hot water. Of course this is kind of drastic, but you can decide if its worthwhile. Plecos are great natural algae control and will rasp wood clean of all but the hardiest of algae. They can get quite large and be a little clumsy so I don't recommended plecos for all setups. There are great choices like clown plecos which tend to stay a little smaller.

Algae Growing on Plants

Just about the saddest sight is watching your prize plant slowly getting overrun by invaders... Here is where patience and persistence really is required. Get your arms in that tank and start pulling as much algae as you can off the plants. Maybe even take the large leaf plants and tougher specimens out of the water and scrape at it with a razor blade. More than just physical removal, this seems to stimulate you algae eating critters. I do not have a definitive explanation for this but I've seen my siamensis ignore staghorn algae until I started ripping it out- then they started really gobbling it up! Maybe it's like peeling an orange for them or something. Keep at it and make sure to get the critters that can help you out.

Algaecides and nuclear warfare

Well, this is an option but we would encourage trying the natural methods first. Of course if you have plants, this is NOT an option. Many claims are made for plant safe algaecides, but this is not our experience. Yeah, anubias will survive but they really could live through nuclear attack, no?

Remember these are ways to deal with algae after they have arrived at your doorstep. Read the article on the causes of algae to address the source rather than the symptoms. There is a lot of chatter about magic pills for algae and there might be valid rationales behind the ideas but really what I think is happening is people try so many things to get rid of algae but only remember the last thing they tried when the algae up and left! Algae eradication is really about a confluence of conditions not the least of which is yes, your patience and persistence.

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