Dealing with Cyanobacteria (Red Slime Algae)

Cyanobacteria - Red Slime AlgaeCyanobacteria or "Red Slime" algae are probably on every reef keeper's top-ten list of biggest problems in their systems. Stories of hobbyists breaking down entire systems, performing huge water changes or even resorting to the use of dangerous medications, only to have the slime quickly return are not uncommon.


Recently, one of my personal tanks became heavily effected so I thought I would take advantage of the situation and write an article with the details of the infection and how I handled it.


In the beginning, I was sure that I had missed nothing in setting up my dream system. I spent months just doing research and planning prior to actually beginning the system. I had a solid plan and I knew I couldn't go wrong.


A few months later, my system was up and running. I fought the temptation to add any livestock early knowing full well that this would only lead to problems done the road.


I went through a brown diatom bloom that subsided as I knew it would, then a green algae bloom that also quickly subsided. It had been nearly 3 months since first filling my system with water. The time was right and my patience paid off.


Over the next few months, my system came alive with new editions. I added very few fish, hoping to keep the nutrient level very low and instead focused on corals and other invertebrates.



My system sported a properly setup plenum with a 4-inch sand bed as described by Bob Goemans (leading authority on plenum use), a dual refugium system, one with about 30 mangroves, the other with various macro-algae, a great skimmer (A Turbo-floter) and a high-output pump that would more than suffice for water turnover. I even constructed an aerating stand to rest my live rock on to ensure there were no dead spots. Additionally, I purchased an RO/DI unit.


My system was perfect. I had set up a solid defense to prevent any invasion of any algae, diatom or cyanobacteria bloom. But guess what?


It had been 10 months since setting the system up. I noticed a small amount of red slime in several spots as well as a very limited amount of hair algae growth. Surely this was just a small bloom that my system was going through which would pass, right? I decided to let it go hoping it would crash on it's own.


Three months later, I realized that I had a serious problem. Not only had the cyanobacteria and hair algae not gone away, they were beginning to gain a solid foot-hold in the main system as well as the refugium. Still not to the point I have seen in other aquariums, I decided to go to war.


My first action was to begin researching everything I could about my enemy. The SUN TZU (The Art of War) says "know your enemy, know your self". Well, I felt pretty comfortable with myself so I figured I would refresh my memory of every minute detail as far as cyanobacteria were concerned.


I needed to know what my enemy needed to survive. After scouring the internet and books alike, I discovered the following:


  • Light (prefers the red spectrum)
  • Nutrients (dissolved organics)

Pretty Basic. So if I turned out my lights and stopped feeding all together, the problem would go away! Well that was out of the question, so I figured I would learn more. Here is some information I learned that I thought was important to note:


  1. Cyanobacteria are photosynthetic and contain Chloropyll A. They require a light source
  2. Cyanobacteria have the ability to produce cells called "akinetes" that store food reserves
  3. One species of Cyanobacteria resemble hair algae. (Lyngbya sp.)
  4. Some forms may bloom in nutrient-poor conditions
  5. Oscillatoria variety (red slime) usually bloom in nutrient rich environments
  6. Most species NOT palatable to many herbivores
  7. Increase Redox potential and elevated alkalinity help to limit Cyanobacteria growth

Hmmmm... number 3 says some forms of cyanobacteria resemble hair algae! Guess what? After a closer look, I discovered this to be my case. I wasn't having a hair algae problem AND a cyanobacteria problem. Just two different cyanobacteria problems at the same time!


#5 says that the species "Oscillatoria" bloom in nutrient rich environments. Well, duh! I knew that already but my tank could not be nutrient rich... could it? The thought wondered through my head for a short time. I couldn't think of any way that heavy nutrients could enter my system. After all, I only have two very small fish in a 125 gallon system! So I decided to take a look at everything that enters my system to try and determine the source.
This is what I came up with:


  1. My hands: Perhaps something is on them when I reach into the tank itself? Definitely would be minor indeed!
  2. Feeding. Normally I feed Formula One or Reef Complete every other night and very carefully. Another very minor possibility
  3. Trace Elements? I'm using B-ionic exclusively which actually helps to prevent algae growth by bringing up and maintaining the pH. Still, I thought it would be a good idea to ensure I wasn't over-dosing. I wasn't.
  4. Salt mix: I'm using Coralife salt as are many of my friends. I looked into it but found no reports of problems with this brand.
  5. Filter Media: I'm using phosphate-free carbon from a very reliable source as well as phosguard. No problem there.
  6. Decaying organisms (usually larger ones in most medium to large systems). Did a check and found a small clam that had died which was quickly removed. Probably didn't help my problem but definitely not a direct cause.
  7. Make-up water. I'm using a DI/RO unit in my home. That couldn't be it... could it?


Perhaps I was on to something. I started to think about my tap water. I knew that in my area, tap water in reef systems could be a problem due to high nutrient content. But I'm using an RO/DI unit! I have been for about a year now, I thought to myself. A year! ...... a year??? Ooops!


I suddenly realized that I never bothered to change my filter cartridges or even find out how often it should be done! Upon researching it, I discovered that the carbon and sediment filters needed changing every few months to help prolong the life of the membrane which did the real work. DOH!!!! I was adding nutrients more and more with each water change and top-off as the filter declined and didn't realize it!


Immediately, I changed my filters and membrane and began kicking myself. I knew I had found the source of my problems but had already allowed the enemy to invade my beautiful paradise! So now that I shut the gates keeping any additional enemies at bay, I needed to figure out how to deal with those who had slipped through.


Common elements from tap-water which lead to algal/diatom/cyanobacteria growth are phosphates, nitrate and silicate. Levels in tap-water for these elements should be as follows:


  • Nitrates:   less than 2 mg/l
  • Phosphates:   less than .05 mg/l
  • Silicate:   .2 mg/l

Remember when I said know your enemy? Well, I had discovered my adversary. It never was the algae, cyanobacteria or diatom growth. They were all just a bi-product of the invasion. Kind' a like burning buildings and lose chickens running everywhere! I had learned how to keep the enemy out, but now I needed to learn how to deal with the enemy within..... my reef aquarium.


Nitrates: A by-product of nitrite and the end product of the nitrogen cycle. Removal from saltwater is simple. Water changes and gaseous exchange. Other than actually replacing the water (which would only be negatively impacted by the remaining cyanobacteria as it died and was removed) my only other option was removal by gaseous exchange. My system had relatively little surface agitation so I added a hang-on back filter to help move the water's surface. Additionally, I purchased a new, more powerful skimmer (a Remora Pro). The Remora Pro worked great and quickly out-performed my Turbo-floter. However, I decided to leave the turbo-floter for now because even though it isn't remove any nutrients through foam production, it is still providing a good amount of gaseous exchange within the skimmer itself. Nitrate Remove was in effect.


Phosphates: Removal of phosphates can be performed in various manner. Aeration similar to that used in removing nitrates helps to remove phosphates so I was on-track there. Additionally, there are various filter medias which effectively remove phosphate. I was already using "Phosguard" so I decided to change it more regularly. I also discovered two things about using kalkwasser (which I had completely stopped using all together some time ago). Firstly, Kalkwasser dosing helps precipitate phosphates out of the water column. Secondly, it helps maintain pH balance, especially if dripped at night. So I began dripping kalkwasser once more but only in the evenings after the lights went out. Phosphate removal was in effect.


Silicates: Diatoms utilize silicates to form their skeletons. I haven't noticed a diatom problem but figure it's best to hit my problem from every area possible so I will include the possibility of having excess silicates as well.  According to Julian Sprung (Algae - A Problem Solver Guide) tap water can have silicates in excess of 50ppm. Therefore, even when utilizing an RO unit that is running at peak efficiency, we may still be adding 5ppm silicates directly to our system! Therefore, for some areas a DI unit as well as an RO unit should be used. Thank goodness I am using both. Additionally, I have ordered a Total Dissolved Solids meter which should arrive soon. This will help me determine if my RO/DI unit is working properly as well as when to replace my filters. The meter cost me about $25.00. Definitely a good buy.


Large water changes can lead to a spike in silicates, as can through excessive feedings. Removing silicates from the system can be done as simply as aggressive protein skimming, utilizing grazing herbivores to eat diatoms as they utilize the silicates and just allowing the silicates time to exhaust themselves. Bottom line, shouldn't be a problem as long as my water source is monitored and insured to be as close to silicate-free as possible.


So what else? I have studied the causes of cyanobacteria, what they need to survive and what direct steps to take to remove their food source (ultimately removing them as well), what else can I do?


The final approach that must not be overlooked is looking for allies of my enemy. So back to researching I go! This is what I found and/or already knew:


  1. Poor lighting assists in cyanobacteria growth a well as other algae growth. Particularly the red scale of the spectrum. My M/H bulbs are about 10 months old so I'm going to replace them. Normally I would wait a full year but found a good deal on eBay so will do it now
  2. Low water movement can provide a safe haven for which cyanobacteria to grow. My system has good water movement (total system capacity should be turned over at least 10 times an hour if not more) however, I will leave no stone unturned! After cleaning and maintenance of every pump and water moving equipment and tubing/hoses, I was surprised to find a nice increase in my water movement. This is something that should be done at least twice a year if not more often depending on system.
  3. High Temperatures can assist as well. My temp remains a constant 78-80 degrees. If your system runs higher (84 degrees or higher) or fluctuates too much, this could be an assister as well. Perhaps the edition of a heater and/or chiller will be the answer for you.


Keep in mind that these 3 items are only assisters in the growth of unwanted or problematic conditions, not direct causes. Eliminating them will not solve the problem, only help alleviate it.


I am happy to report that after only a few short weeks, my cyanobacteria is almost gone. The Oscillatoria variety seems to be completely eradicated, and the Lyngbya variety (which I had originally thought to be hair algae) is well on it's way.




After reading this article, I hope you as well are on your way to beating this problem. Here are some additional pointers to keep in mind when fighting a bloom or trying to avoid one:


  1. Never disturb your deep sand bed. This goes for plenums as well. Using a turkey baster or powerhead to gently blow the uppermost surface is fine but sand stirring is actually counter productive and can even lead to the problem itself by releasing harmful elements and organics (if improperly maintained) as well as damaging your sand bed!
  2. Always remove as much of the cyanobacteria as you manually can. This will help speed up the process. After all, removing the cyanobacteria is essentially removing the harmful elements and organics as well. This may be a daily process and might even get a bit repetitive, however it is none-the-less, very important. You will find over time, that it will be harder and harder for you to find any to remove at all!
  3. Keep a close eye on your system for dead and decaying organisms. This is especially true for smaller systems.
  4. Keep your skimmer clean! I remove my skimmer cup DAILY and completely clean it. I also use a brush to thoroughly clean the inside of the skimmer itself! A neglected skimmer is a wasted piece of equipment and one that you should not do without!
  5. Don't hesitate to replace any DI/RO filters. They are extremely cheap. The alternative is replacing the RO/DI membrane which is not nearly as cheap. Trust me on this one (for those of us using our own DI/RO unites)
  6. Never take for granted that the water you are using from the local fish store is free of contaminants. Test it from time to time to make sure! Even experts forget to change their filters!
  7. Ensure that you keep your filter media clean and fresh. I change mine at least once every two weeks.
  8. It's a good idea to add a little live sand and a few new members to your clean-up crew from time to time. This will go a long way in preventing problems in the future.
  9. Completely remove all of your pumps and powerheads on a routine basis. They really do partially clog more often than you may think!
  10. Stay away from medications or miracle cures of any kind! They are harmful to your system, especially the beneficial bacteria our systems need to survive!
  11. Keep your pH up, especially during the evenings.
  12. Hang in there! Your problem will not go away overnight but if you follow what I have laid out here, you'll find that in a very short time, things will be back to normal.