Destroying Algae in a Reef Tank

Posted by jared burbank on

The ultimate goal of reefers is a crystal clear tank, with vibrant coral throughout the tank, and thriving fish whisking from one side to the other.  Oftentimes this is easier said than done, but are you really doing everything you can to achieve this goal? 


If you get a film on your glass daily, have hair algae growing on your rocks, or your sand bed just looks dirty, you know what I’m talking about.  The tank just doesn’t look clean, but there are things we can do to alleviate these issues.


Algae is one of the most common issues that reefers face.  It thrives on the excess nutrients in our system, so if you have algae growing like crazy in your tank, it’s a given that you have excessive nutrients in your system.  I don’t know how many times I’ve heard people complain about algae, and then say that they’ve tested their water and everything is perfect – but your water is not going to test abnormally high if you have algae growing everywhere because it is consuming it as it grows.


So how can we get rid of those extra nutrients in our system?  This comes in two methods: first prevention, and second, removal.  When addressing prevention, we have to look at everything we are adding to our system that is feeding the algae.  In most cases, that is the food that we feed the fish and/or coral.  Do we really need to feed them as much as we do?  In my opinion, I would say most people overfeed their systems. 


  • Judging your fish feeding: Remember that a fish’s stomach is about the size of their eyeball. Look at your fish, and really judge if you are overfeeding.  Yes, when you go up to your tank they will come running up and give you a sob story about how they are starving, but there is a good chance that you are overfeeding them.  Any uneaten food will decay in the system, plus the more the fish eat, the more they poop - and if you feed in excess, the food will go through their system faster with less nutrients being removed, which causes more pollution in your water.


  • Coral Feeding: Do you feed your coral, and do you really need to? Yes, we all want to see our coral explode in our tanks and double in size quickly, but is that extra coral food we are adding to our tanks really being consumed by them, or is it just polluting our system and contributing to the algae problem?  We’ve been growing coral for over a decade, and except for a handful of specific coral types that require direct feeding (sun coral and dendros among them), they don’t really need to be fed directly.  Chances are if you are feeding a “coral food” to your tank, the majority of that food is just going to waste and polluting your water, which is a huge contributor to algae.  When we feed the fish in our tanks, what the coral get is what they get, and they benefit from the better water quality and grow fantastic for us.    


  • Using a good protein skimmer: A protein skimmer is one of the best ways to remove extra nutrients from your system. The skimmer works with the injection thousands of micro bubbles into a chamber, and the proteins will attach to the bubble walls that develop into a foam, which will then overflow into collection cup. The skimmate collected can then be discarded, thus eliminating the decaying protein from your system.  A protein skimmer is a real workhorse, and I always recommend that you use a high quality skimmer that is well overrated for your system. 



  • Biopellets: Biopellets are a form of carbon dosing, and in conjunction with a quality skimmer can increase the removal of proteins from your system. Biopellets are made primarily of a biodegradable polymer that will feed and increase the growth of bacteria cultures in the system.  The bacteria will help consume extra nutrients in the system, and when this bacteria dies off it will be removed by the skimmer.  Biopellets preform the same function of carbon dosing, and incorporating them is a great way to increase your skimmer’s performance.



  • Granular Ferric Oxide (GFO): Algae also feeds on phosphates in your tank. Using GFO is another option if you are battling phosphates in your system. It can be run in a reactor or a mesh bag in a higher flow area of your sump. GFO actually forms a chemical ionic bond with phosphates in your system, and strips it directly from the water. With GFO, start slow with a small amount (about ¼ of the recommended amount), as you never want to make drastic changes to your system.  You can add additional if needed weekly, but do take it slow. Care should always be taken when using GFO, as it can also remove alkalinity and other trace elements from the water.



  • Refugium: Since our goal is to remove algae from our tank, we can turn the table on it and grow algae elsewhere hidden in our sump or refugium.  The process requires having a chamber in the sump dedicated to growing an algae such as chaetomorpha, calupra, or other macro algea to consume nutrients from the system and help prevent the algae from growing in the display tank itself.  This macro can then be trimmed back and disposed of removing the nutrients they consumed from the system. 



  • Chaeto Reactors: Chaeto reactors are new on the scene and work just like a refugium.  It is just a clear reactor chamber with a light strip wrapped around it that is tied to the system and chaeto is grown it in.  Once the chaeto fills the chamber the majority is disposed of removing those nutrients from the system.  While these are relatively new there are only a couple of manufactures of them but they are easy to DIY using an old reactor chamber.



  • Algae Scrubbers: The process is very similar to a refugium, we want to grow algae in an area away from our display tank but in this instance we are growing hair algae on a screen.  Water is pumped up and then trickles down onto a screen that has light shining onto it where the algae grows. The screen is then removed and cleaned periodically.  This helps choke out the excess nutrients by consuming them in the scrubber.


  • Critters: Of course there are a plethora of fish and intervertbrates that can help eat algae you're your tank. Most tangs are very aggressive at eating algae from a display tank, some blennies, lettuce nudibranches, and a healthy clean up crew of snails and/or hermit crabs to help to consume it as well. This doesn’t address the cause of the excess nutrients though and should be used in conjunction with other methods address above.


  • Water Changes: And the single best way to remove excess nutrients from a system is water changes.  With water changes you remove the excessive nutrients from water removed and replace with clean nutrient free water.  Remember if you do a 10% water change it only lowers your nutrient problem by 10%. Don’t be afraid to do larger and more frequent water changes until you the problem under control. 


When faced with an algae problem I like to address it on multiple fronts.  First I’ll work on direct removal on excess nutrients by aggressive water changes, reduced feedings, making sure my skimmer is working at it’s full potential.  Then I might institute a chaeto reactor, algae scrubber, and maybe even some GFO.  Following this I’ll often see the algae start to die or getting stringy from lack of nutrients.  I’ll get aggressive and take a tooth brush and really scrub down the rockwork to manually remove as much of the algae from the system as I can.  I will also blow out the rockwork with a powerhead every few days to remove all the buildup in the rocks that can help feed the algae in the tank.  I’ll then add a bunch to my clean up crew in the way of snails, hermits or other algae eating critters to help clean up the leftover algae.  Within two or three weeks I will see a marked reduction of algae in the tank.  From here it’s just a matter of maintaining the system to prevent excess nutrients and keep the algae at bay.  It is really not difficult, and makes a huge difference in the enjoyment of the aquarium.