How to Control Algae in an Aquarium

At some point in nearly every aquariums life, there will be algae growth.  It is common and normal. Some algae, such as blue green algae, is even beneficial in small quantities as it contributes to the health of the nitrogen cycle.

However, in large quantities, algae is aesthetically displeasing, ugly, and can be unhealthy.  This article will cover how to control algae in an aquarium though prevention before algae takes over and through treatment after algae has overgrown the tank.

Preventing Algae

In nearly every case, it is easier to prevent algae growth than it is to treat it.  Routine maintenance will typically head off any excessive algae growth before it becomes an issue.

Excessive feeding can contribute to algae growth.  So keep with the rule of thumb for feeding – no more than your fish can eat in a 2-3 minutes several times a day. Uneaten food decays into ammonia which goes through the nitrogen cycle and ends up as nitrates. Nitrates are food for algae and an excessive amount will help to produce and environment that is appropriate for excessive algae reproduction.

Excessive feeding can also result in overeating.  A fish that has overeaten will excrete more waste which will go through the nitrogen cycle also contributing to excessive nitrates.

As part of your routine maintenance, scrape excessive algae from the inside of the aquarium glass.  This not only reduces the population of algae, but it keeps you tank clean and better for viewing.  The excessive algae that was removed should be vacuumed up during your water change.

Do a weekly water change.  This will help to keep nitrates, phosphates, and silicate levels low.  These are all food for algae and excessive levels of these compounds can result in excessive algae levels.  Water changes also remove algae that is suspended in the water.  Removing and replacing 10-15% of the water will help to reduce the number of algae cells that can reproduce.

During your water change, you should vacuum up any extra food or waste that is in the gravel.  Also, be sure to vacuum the algae that you scraped off of your glass.  All of this excessive “junk” will ultimately decay and go through the nitrogen cycle resulting in high levels of nitrates.

Light levels are also critical for controlling the growth of algae.  Algae relies on photosynthesis, just as plants do, to produce energy.  With excessive levels of light, algae has extra energy with which to reproduce.

Aquariums should never be placed in direct sunlight.  Even indirect sunlight can contribute to excessive algae growth.  Also, your aquarium lights should be on for no more than about 12 to 14 hours.  It’s easiest to buy a light timer and plug your lights into it to keep everything automated and on an appropriate schedule.

A few other items that can contribute to excessive algae are stagnant water and an overpopulated tank.  Algae has a tough time growing moving water. Most filters do a good job of keeping your water flow up, but if your filter is small or your tank is long, you may want to invest in a powerhead, which pumps water to create a small current.

Treating Algae

Micropix [CC BY-SA 3.0]
Micropix [CC BY-SA 3.0]

If your tank already has been overtaken by algae, you may have a bit of a difficult task ahead of you.  Removing algae can be significantly more difficult than preventing it.

Some algae removal is easy.  For example, brown algae often shows up during the initial cycle of the tank and will go away on its own as the tank establishes itself.

If you’ve been following proper maintenance and doing everything that’s listed above, you should test your tap water for phosphates and silicates.  If you find elevated levels, you should replace your filter media with phosphates and/or silicate media as needed to neutralize your water as it’s added to your tank.

If you’ve tested your tap water and find nothing wrong, you should start by doing a large water change. This should help to immediately reduce the population of the algae.

Next up, you should do a total blackout of your aquarium for several days.  Turn the lights off.  If the room with your aquarium is naturally bright, you should cover your aquarium to block out all light from getting into your tank.  Cover it with a blanket or some towels.

Algae relies on light for energy through photosynthesis.  By removing the light, you have removed their food source and eventually you will starve them out.

Check your tank after several days.  As your algae dies off, you should do a water change.  Dead algae will decay and go through the nitrogen cycle.  If you don’t do a water change, the resulting nitrates will contribute to more algae growth.

Chemical for Algae Treatment

There are many chemical treatments that work to kill algae.  They tend to work well.  They also tend to work quickly.  This can result in dead algae getting into the nitrogen cycle quickly.  And quickly adding to the problem.

UV Sterilizer for Algae Prevention and Removal

The most surefire way to kill all algae and prevent future growth is with a UV sterilizer.  UV sterilizers operate by blasting ultraviolet light into the water.  The ultraviolet radiation kills any algae it makes contact with.  Note that most UV sterilizers pump water through a device which contains the UV rays and doesn’t allow any light out so it’s safe for humans and fish.