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Cyano-ra: Say Goodbye to Nuisance Algae

When most reef hobbyists talk of cyanobacteria, it would seem that they are talking about red film algae. Actually, cyanobacteria are blue-green slime or grease algae. Red film algae, the type that grows in mats on Red Algaesubstrates and over animals, is just as much a nuisance as cyanobacteria. Therefore, this article will focus on limiting nuisance algae in the reef aquarium. The things we can do are numerous, and some, most, or all might be necessary for your system.

Protein Skimming

In the book "Marine Reef Aquarium Handbook," Dr. Robert J. Goldstein states, "Among the most important nutrients for cyanobacteria are the dissolved organics secreted by the microbial biofilm and algal mats. Foam fractionization (protein skimming) reduces dissolved organics in water, removing the very substances that promote cyanobacteria, shifting the advantage to red and green algae." What this statement goes to say is, if you are not using a protein skimmer and you are suffering a nuisance algae problem, then you should be. So step 1, get a skimmer.

Maintenance Animals

A well rounded reef tank should contain some number of maintenances animals that feed on detritus and algae. They help keep the nutrients mobilized and help to keep algae in check. Most, however, will have nothing to do with the red nuisance algae as the red algae contain some chemicals that discourage herbivores. But for browns, greens, and blue-greens, get some janitors. One turbo or astrea snail per 2 gallons, 1 blue-leg hermit per gallon, and a couple of Sally Lightfoot mangrove crabs per system should go along way in keeping nuisance algae in check. If valonia (bubble algae) is a problem, a green mithrax crab will do the trick.

Limiting Nutrients

Nuisance algae do not overcome the open reefs because of the limited amounts of nutrients available. Therefore, limiting nutrients in your tank will also aid in algae control. Nuisance algae thrives on nitrate, phosphates, and silicate. Reducing these components will help arrest a nuisance algae problem.

A first step toward limiting nutrients could be to add more water flow. This helps to keep the nutrients suspended in the water column so that mechanical filtration and protein skimming can remove them. A good rule of thumb is a combined flow rate of 10-20 times tank capacity. That would be 1000-2000 gallons per hour in a 100-gallon tank.

Housekeeping Chores

A good way to limit the nutrients in a reef tank is to introduce very little into the tank. Feed your fish and corals lightly. The reef is not a never-ending smorgasbord. Stock a reef with only a few fish, and then only feed what they can consume in 1-3 minutes, once a day. Don't worry, they will be fine.

Now that you have added the food, do what you can to get it out. Occasionally vacuum your sand bed, if any, or if you have a bare-bottom tank, vacuum it regularly. Get the detritus out before it adds to the algae food. Also, harvest whatever algae you can by hand and remove it from the tank.

Also, stop adding supplements, particularly iodine, until you have the situation under control. These supplements can easily aggravate a nuisance algae problem.


Nitrates can be controlled with either a deep live sand bed, or frequent water changes, so long as the water used to execute the water change does not contain nitrates. Use Reverse Osmosis (RO) or De-Ionized (DI) water to ensure you are not exacerbating the problem with your tap water.


Phosphates are introduced into the tank as foods breakdown, and in tap water used to do water changes. As stated earlier, feed lightly, and use either RO or DI water for your water changes and for top-off water. Also, if you will use Kalkwasser (lime water) for your top-off water, it will help to precipitate phosphate out of the water column. Lastly, a phosphate "sponge" can be used to effect the chemical filtration of phosphate.


Silicates are often found in well water, and from other sources. RO does nothing to limit silicates, but DI controls phosphate, nitrate, and silicates. Therefore, I would recommend DI for everyone. The Tap Water Purifier from Aquarium Pharmaceuticals is a cheap starter kit for a DI system.


As bulbs age, their color tends to shift towards the red spectrum. This color shift encourages the red algae. Therefore, you need to change your bulbs regularly. (See the section on lighting for the intervals of different types of lighting.)

In summary, there are several things that you can do to rid your tank of nuisance algae, and most of them are probably good ideas anyway. Listed below is a recap of those items:

  • Protein skimming
  • Maintenance animals
  • Increased flow
  • Feed lightly
  • Vacuum substrate or bottom
  • Harvest algae
  • Stop adding supplements
  • Regular water changes
  • Use RO/DI water
  • Top-off with Kalkwasser
  • Regular bulb changes

If you implement these things, you can say cyano-ra to nuisance algae.


Copyright © 1999-2000, Scott Brown, except as otherwise noted. All rights reserved. This work may not be reproduced, in part, or in full, without the express written consent of the copyright holder.