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How do I get rid of algae in my fish tank?

All fish tanks need algae to survive. When we talk about getting rid of algae, we aren’t talking about essential algae, or macro algae like caulerpa, we’re talking about nuance algae. Especially prevalent in this discussion are hair algae and beard algae. This article will discuss what causes algae to grow to nuisance levels and what to do about it. There are quick fixes to getting rid of algae, but no quick fixes for keeping it gone (more on that below).

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Is algae in my tank harmful?

Many living things in both freshwater and marine tanks (such as snails) eat algae, and would perish if there was none in your tank at all.  Therefore, getting rid of all algae is not the goal and some algae is not harmful. However, excessive algae can cause numerous problems, especially in a planted or reef tank.

What most of us don’t like about algae is simply that it isn’t very attractive, grows on our rock and other decoration, and causes us extra work. For the most part, other than just being a bother, the algae in your tank in not harmful.  However, as mentioned, it can create certain conditions in your tank that will cause harm.

Algae in Tank

Below are a few things you are likely to experience where algae can can cause problems.

  • Can grow on filter intake and outtake fittings reducing filtration
  • Can grow on power heads reducing flow
  • Can reduce the amount of light entering the tank reducing the amount that gets to plants or corals
  • Can grow directly on plants or corals reducing their ability to photosynthesize or causing irritation to coral tissues and bleaching
  • Can compete with decorative macro algae for resources causing it to fail
  • Can alter the pH level in your tank

The above means there is a reason to keep algae at a minimum in your tank other than just the fact it is unsightly. If all you have

Why is there algae in my tank?

Algae is in your tank because conditions in your tank are right to promote its growth. There’s plenty of light, and nutrients for the algae to use as a food source and thus proliferate.

It’s clear where the light comes from, but where do the nutrients come from? They come from the food you put in the tank and the waste produced by the livestock. Therefore over feeding, and overstocking a tank can increase the algal growth dramatically.

The main nutrients to blame are phosphates and nitrates. In planted tanks algae can often be a byproduct of not enough carbon dioxide. This might seem odd since Co2 is a nutrient. How could not enough of it make algae grow? This is because of the relationship of the C02 to the plants in the tank. There are numerous articles to be found

How can I remove algae from my tank?

You can manually remove the algae with a scraper or scrubber of some sort.  Make sure if your tank is made from acrylic that the tool you use is safe and won’t scratch the tank surface.  Many nice tanks have been ruined in this way.

Another method is using livestock to remove the algae for you. Certain snails, crabs, shrimp and fish eat algae, by having the right “clean up crew” in your tank they can do much of the work for you, usually leaving just a bit on the glass to be easily removed. Choose wisely because the clean up crew becomes part of the bio-load in the tank and can actually increase the nutrients that lead to the algae in the first place.

How can I keep algae from growing in my tank?

Of course scraping algae off the sides of your tank gets it off the glass, but when you want to know how to get rid of algae, that’s probably not what you mean, you’re probably thinking of a more long term solution, something to keep algae at a minimum.

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Below are the basic steps you can take and the pros and/or cons of each. Too much of any one method can cause problems in the tank, but by using some of each method.

  • Wait for it to go away on its own
    • Pros:
      • If the tank is newer the algal bloom may just be a result of the natural cycling process and will take care of itself.
    • Cons:
      • If the bloom is not part of the regular cycle of a new tank it will continue to grow while you wait.
  • Poison the algae with a commercial algaecide such as Algae Control, 100 ML by Tetra brand.
    • Pros:
      •  It will kill the algae.
    • Cons:
      • It will kill the algae, all of it.  Some algae is beneficial to your tank and you don’t want it all gone.
      • Many algaecide are copper-based.  Copper is bad for invertebrates, so much in fact, that it kills them.  If you have snails, shrimp, or other invertebrates you are risking them.  In a freshwater tank, you are may not have any.  However, in a reef tank you will have all sorts of worms, amphipods, and other micro-fauna that could be adversely affected.
      • Some algaecide reduce the oxygen content on your tank which can adversely affect your fish.

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  • Reduce the amount of light in your tank either by reducing the amount of time it is on or by reducing the wattage.
    • Pros:
      • This is a very easy method.  By starving the algae of light they will die off.
      • You will reduce heat and save electricity.
    • Cons:
      • If you have a planted tank this will be harmful to the plants that require more light.
      • In a reef tank this may not at all be possible since many corals require light to live.
  • reduce the amount of food you feed the fish. Of course you have to make sure the fish have enough to eat, but make sure it isn’t too much.
    • Pros:
      • Again, this is a very easy method.
      • You will save money on fish food.
    • Cons:
      • Some fish require frequent feedings or do better when feed several times a day. Reducing the amount of food you give your tank can cause your fish not to thrive.
      • Less food in the tank means less leftovers for scavengers like hermit crabs and worms. In some cases this can cause them to seek food elsewhere, which may mean they nip corals or attack fish.
  • more frequent water changes.
    • Pros:
      • Regular water changes are a good idea to begin with so this will simply help you keep a regular schedule.
    • Cons:
      • Too frequent water changes can alter the levels of elements in the water, such as calcium and can also reduce the beneficial bacteria in the tank.
      • If you have a marine tank this means you will spend a bit more money on salt mix.
      • Water his heavy and water changes are work.  While this sounds like a silly con, over time, it really does become a chore.
  • check your filter/protein skimmer to make sure they are working well enough for the size tank you have.
    • Pros:
      • Proper filter maintenance is a must.
      • Having the right equipment for your tank can make all the difference.
    • Cons:
      • If you find you have the wrong filter you will have to spend money on a replacement and go through the process of cycling it.
      • If you don’t have a protein skimmer for your marine tank, you will have to spend the considerable amount of money required to buy one. We do think a protein skimmer is an important part of a reef tank.
  • Add a macro-algae like halimeda or caulerpa to out-compete the micro-algae.
    • Pros:
      • This is an affordable method that produces lots of benefits. It helps to balance pH in a tank, uptakes nutrients into the algae which can then be harvested and removed from the tank. This also creates an environment in which useful creatures like pods can thrive. This is a method I have used for years and which I find very satisfying.
    • Cons:
      • Some macro-algae can be as much of a problem as micro-algae in terms of prolific growth. For that reason this solution is best used if you have a sump or if the main tank is meant to be biotope of caulerpa.
      • Some macro-algae have cycles wherein they dump all of their chlorophyll into the tank causing a dramatic reduction in oxygen.  In smaller tanks, this can kill off all inhabitants. In larger tanks it will turn the water green and require a water change along with some carbon and GFO. If this happens it pretty much negates the purpose of growing the algae. I’ve only had this happen once. That was with halimeda. It was in a 5.5 gallon tank so it turned utterly green.
  • Add an ultraviolet sterilizer
    • Pros:
      • Generally quite effective in killing micro-algae.
    • Cons:
      • Can reduce algae too much not leaving enough for algae eaters to survive on.
      • Requires installation, a power source, and maintenance.
      • Can be expensive to purchase.
      • Will require replacement bulbs from time to time.


What the best solutions really come down to is reducing the bio-load. Waste builds up nutrients which the algae feed off of and in turn grow out of control. Find a way to reduce the bio-load and you will have success in reducing algae. Adding creatures to eat the algae only works if they can eat fast than it grows. Those creatures add to the bio-load and thus add to the problem. Algae control products do kill algae for sure but they don’t reduce the bio-load. In fact, they can add to it if you don’t do a water change right away. All that dead algae breaks apart as it decays and all the nutrients contained inside suddenly gets released. Thus providing food for future generations of algae. So, while you get rid of the algae in the short term make sure you take care of the overall problems for the long run.