Controlling Nitrates with Chaeto?

by Justin Hester

Show most reef aquarists a picture of squiggly algae and 90% would probably call out the name chaetomorpha or “chaeto”  as its commonly known.  Many of us use this algae to export nutrients in the form of Nitrate and phosphate from our reef systems.  Knowing how much you need to keep though has always been kind of a mystery and depends on many factors in your tank.  Through some experimentation, we have documented at least what we have seen in our tanks and hopefully it can act as a guideline for others wondering about how much chaeto they need in their tanks and how to find that perfect balance.

How do Nitrates enter the Reef Aquarium and what can they do?

If you had to sum up the world of reef keeping in one word, it would probably be balance.  Those of us that have kept a reef tank for a long time know that no matter which of the dozen parameters we monitor for our tanks’ health, keeping them steady is almost as important as keeping them within the right range.  Nitrates fall into the category of being both a little challenging to test, yet having a direct impact on coral health and growth.  Finding their source and removing them can be challenge even for the most experienced reef aquarist.  Doing so successfully though can help your corals’ long term health. 


Where do nitrates come from?

POOP! Literally, if you walk through the nitrogen cycle that operates in the background of all reef aquariums, the cycle of feeding our creatures, having their waste ( Amonia NH4) converted to nitrite (NO2) and later Nitrate (NO3) is the most fundamental of equations we need to know.  Its also the source or most of the nitrate in our reef aquariums. If left unchecked, Nitrate in particular can creep up over time and  cause all sorts of issues in your reef tank.

Increased nitrate levels can lead to a browning of your corals as the nitrate basically acts as fertilizer for the zooxanthellae algae that grow in their tissues.  As this layer of algae grows thicker, the bright colors you are used to in your corals will become dull and dark hiding your corals true colors.  Taken even higher, nitrates can lead to corals dying altogether.

What is Chaetomorpha?

Chaetomorpha is a single celled algae that lives in many areas of the oceans around the world. Its growth form resembles a corkscrew of strings and looks much like a piece of steel wool or pasta. The most common species of Chaetomoprha or Chaeto (pronounced cato) as it is often called is Chaetomorpha linum. Chaeto is different than most other algae that are grown in reef aquariums in two ways. First, they are made up of single tubular strands of cells that are connected end to end which makes them fast growing and increases their surface area very quickly. Second, they do not contain the turpin compounds that most other macro algae have. The lack of these turpins and thus the inability to slow coral growth make these algae the preferred type to use in a reef aquarium or refugium. When you go to pull it out or remove it, there aren’t any holdfasts or roots to contend with either.  It just comes out in a twisted handful which makes it easy to remove and share with your fellow reefers. For more info on chaeto, we also have a full article dedicated to its use in the marine aquarium.





How can Chaeto be used to reduce Nitrates?

Perhaps the characteristic that makes Chaeto most desirable to the reef  aquarist is its ability to sequester nitrates and phosphates into its cell structure.  This occurs when the algae simply uses these compounds as food for its general biologic processes.   Once it has done that, removing these from our systems is as easy as grabbing it in handfuls and removing it. This makes a great cheap and simple alternative to many of the absorbing medias, chemicals, as well as reducing the frequency of water changes.  Just think about how much you spend on these products and maybe you will find some value in using that money to setup a small refugium with a light!

How much Chaeto is enough for Nitrate balance?

Nitrate balance using chaeto is a 3 leg seesaw.  On one leg, you have the energy input that starts with you feeding your tank food.  On the second, you have the Nitrogen Cycle, where bacteria convert the waste products (NH4) into nitrate (NO3).  Finally, you have your chaeto which is there to remove that nitrate from the system entirely.

Now, when it comes to gauging how much chaeto you need to grow, unfortunately I don’t have any magic answer for you, but I do have a process we use and I think it might be helpful!  That being said, having more than less chaeto is always better. You will also be able to gauge how much chaeto you need to grow, by monitoring your nitrates closely. You will notice them dropping not only from the chaeto, but also from your weekly water changes.  The drop from the water changes will however be a sharp spike, while the chaeto will either have no effect, a maintaining, or slight lowering effect on your nitrates.

Rising Nitrates after adding chaeto

If you add chaeto and nitrate keeps rising or is crazy high, you know you don’t have enough chaeto or room for it to grow.  You can typically see when the chaeto has grown to the capacity of its container and is could literally be taken out and hold the shape of the container.  This basically means, there is an excess of food (nitrates) in your tank and you should probably expand your area for growing chaeto as well as take a hard look at how much food you are feeding your fishies!

nitrate decrease after adding chaeto

A slight lowering comes from having more than enough chaeto to consume the nitrate that is being produced in the nitrogen cycle. In this scenario, you will typically see your ball of chaeto stay at the current size it is and maybe even waste away a little as the nitrate levels approach 0.  Remember, even without nitrate to fertilize the chaeto, it can still make food for itself through photosynthesis and thus shouldn’t die completely.

Steady nitrates after adding chaeto

What if you find yourself in nitrate nirvana and you see your levels hold steady?   First, go buy a lottery ticket as you are one lucky reefer!  This means that you have dialed in a perfect amount of chaeto to offset the nitrates created by the nitrogen cycle.  If this leveling happens with a bit more nitrate than you would like, you can simply dial it in further through a water change or two.  I will say this this situation is rare since our reef tanks are systems and not controlled environments.  There are so many little variations that can effect this process that maintaining nitrates should most often resemble the “slight lowering”  model discussed above.

Once you have nitrates under control, your tank should be relatively free of nasty hair algae and any visible cyano bacteria and remain so for some time.  As your tank matures over the years, this method is also a useful way to keep your sand bed super thin and avoid old tank syndrome.  Keep in mind, as you change your nitrate load with feeding variations or the addition of fish and corals to your tank, your chaeto with expand and shrink with the nutrient load.  With the Chaeto, you don’t need such deep sand bed for anoxic denitrifying bacteria to live in so you can also avoid buildup of any other waste products here.

EAT sleep REEF repeat!

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