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Cyanobacteria; Blue Green/Red Slime Algae in Aquariums & Ponds

Cyanobacteria (Red/Orange Slime, Blue Green Algae) in Aquariums, as well as related studies in this bacterial plague affecting lakes and other natural bodies of water and how this research can relate to aquariums.

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By Carl Strohmeyer
Updated 1/22/19

This article starts off with a generalized section about Blue- green algae (Cyanobacteria) blooms (mostly in lakes), then goes into more depth about Cyanobacteria and finally aquarium applications/treatments.

FORWARD FROM GENERAL RESEARCH (not necessarily aquariums):

Blue Green Algae, Cyanobacteria

First, over the years, I have dealt with Blue-Green Algae (Cyanobacteria) many times in my aquarium maintenance business. The key to eradication is finding the root cause, understanding it, and then correcting it.
We also have a lot of Blue Green Algae problems here in the lakes of Oregon (it's not even a true algae, rather modified bacteria; Cyanobacteria). I understand that the out breaks are different from aquariums, but there are similarities too. I've done some research on this subject, including reading the local newspapers about treatment and control in our local lakes.


A few points from my Aquarium Research and General Cyanobacteria Research:

(1) Lighting- most research seems to indicate that the type of light affects the growth of Cyanobacteria. In fact, effective PAR light that is less in the yellow nanometers bands may be one of the major factors in control of Blue/Green, Red Slime Algae growth. This is in both salt and fresh water. In controlled experiments with Fluorescent and 6500K lights, changing to true noon-time tropical sun 6500K lighting reduced the amount of Cyanobacteria.

As well, I've noted that many freshwater lake Cyanobacterial outbreaks happen around June and July. In the more northern latitudes (often around the 45th parallel) the lighting factor here will be more affected by seasonal changes in light than middle latitudes.
Cyanobacteria utilize light in regions with low near infrared. These bacteria make use of the unusable light discarded by the plant kingdom, in this case, light outside the PAR range required by plants (technically PUR). This is why Cyanobacteria thrive in lighting conditions that include the more yellow 4000 K and below and why actinic as well as BALANCED light in the 6500 K range keep this bacteria from thriving.

Research shows that while most plants utilize light at 435nm and 675nm (again the primary “spikes” in PAR known as PUR), Red Slime Cyanobacteria (& other Red True Algae), utilize more of the middle yellow and green light spectrum that is most common in poor fluorescent and incandescent lighting; this is an important point.

What is also key is not all 6500K lights are equal as just as with paint, different light spectrums ("colors") can be mixed to make a specific Kelvin color temperature.
"High End" LED fixtures such as TMC AquaBeam and GroBeam models have spectrums with much less of this useless light spectrum that Cyanobacteria thrive on. Unfortunately many of the popular LED sold by discounters such as the Current Satellite, Fluval, & Finnex have much of their light in the middle spectrums preferred by Cyanobacteria due to their mix of emitters. The use of warm while lights or emitters are like cyanobacteria "magnets" based on my experience.
Product Resource:
TMC AquaBeam and GroBeam LED Lights

6500K Fluorescent aquarium lights with different light spectrums
As well even fluorescent lights that start out with reasonable spectrums WILL degrade and after one year of normal use (on/off 12 hour cycles) with much more yellow light that again Cyanobacteria thrive on. So replacing your fluorescent lights annually is important.
The picture to the left demonstrates the factual difference in light spectrum in two 6500K lights, one new and one older (click to enlarge).

Unfortunately I have read some Reef Keeping forum posts arguing that there is no difference in light spectrums of lights of the same Kelvin temperature claiming this is a miss-understanding of light Kelvin; however simple Spectrograms show this is a patently false statement as spectrums from two 6500K or other Kelvin light is often different, whether it be an older versus newer version of the same light or two different brands of 6500K, 10,000K, etc. LED lights!

A study I have conducted (although limited) with a marine tank with a history of Red Slime Cyanobacteria:

For this reason it is important to improve your overhead lighting (especially marine aquariums), in particular the type of PAR output. Get rid of the mid range color output (many fluorescents, even power compacts still have much of this mid range yellow light) and increase strong daylight with; Aqua Ray LED Lights and/or Metal Halide.

A resource for: New generation, full spectrum LED aquarium lighting from AAP

The Compact Fluorescents, SHO daylight, T5, or T2 daylight are still an improvement over older style T8 & T12.
This is especially true when full spectrum 6400-6700K lights are used (not the 10,000 K often recommended), However, as my tests showed, even switching out with these more advanced fluorescent lights did NOT achieve the dramatic results that high percentage PUR LED lighting produced (only slight improvements).

A lighting resource:
Helios new generation VHO bulbs, fixtures
SHO, super high output bulbs
Clamp on LED Aquarium Lights

In saltwater aquariums, a simple improvement in overhead lighting, good vacuuming procedures, and a additional UV Sterilization (properly installed) will rid the tank of this problem most of the time.

With ponds, make sure opaque awnings that block UVB while primarily allowing yellow and green light spectrums are not used.

For further information about lighting, please read this article: Aquarium Lighting

(2) Heat/Water Flow- In high summer temperatures with poor in and out flow of water, this will induce an outbreak. This also may relate to the Redox Potential (Balance), I recommend reading more about this here:
THE REDOX POTENTIAL IN AQUARIUMS (& PONDS); and how it relates to proper aquatic health

Fresh water and good Redox Balance seems to play major a role. In lakes this bloom will usually coincide with poor inflow and outflow of water. This also causes a change in trace element content as well as Redox. This can then be applied to aquariums; in maintaining regular water changes, maintaining a GH over 100 ppm (for calcium and trace elements), as well as correct Redox Balance (UV Sterilization helps here too). Applying this knowledge can be an important part of the Cyanobacteria eradication puzzle as some of my observations/experiments have shown.

(3) Nutrients- The amount of nitrogen based and phosphate nutrients need to be reduced.

As this relates to aquariums, I would increase circulation, clean and vacuum the bottom every other day, cover the aquarium from light for three days, reduce the temperature, consider UV Sterilization to kill free floating cyanobacterium, and reduce the nutrient level.


Cyanobacteria, many forms, Anabva, Microcy, bloom Knowing more about this “algae” is important for eradication.

Going deeper-

Though Cyanobacteria do not have a great diversity of forms and though they are microscopic, they are rich in chemical diversity. Cyanobacteria get their name from the bluish pigment Phycocyanin, which they use to capture light for photosynthesis.
Phycocyanin is a Phycobilins which are useful to organisms that use them for soaking up light energy.
They also contain Chlorophyll; the same photosynthetic pigment that plants use. In fact the Chloroplast in plants is a symbiotic cyanobacterium, taken up by a green algal ancestor of the plants sometime in the Precambrian.

However, not all "blue-green" bacteria are blue; some common forms are red or pink from the pigment Phycoerythrin. These bacterium are often found growing on greenhouse glass or around sinks and drains. The Red Sea gets its name from occasional blooms of a reddish species of Oscillatoria, and African flamingos get their pink color from eating Spirulina.

Whatever their color, Cyanobacteria are Photosynthetic, and can manufacture their own food. This has caused them to be dubbed "blue-green algae", though they have no relationship to any of the various eukayotic algae. The term "algae" merely refers to any aquatic organisms capable of photosynthesis.
Cyanobacteria are aquatic and photosynthetic, which means, these bacterium live in the water and can manufacture their own food. Because they are bacteria, not algae, they are quite small and usually unicellular, though they often grow in colonies large enough to see.
Blue Green Algae (Cyanobacteria) can look a lot like actual true algae, however when it grows on the sides, decorations, and substrate of aquariums it has a much more “slimy” mat appearance and will easily “brush off’ or even come off with a medium to strong water current. This is generally NOT the case for true algae.

Cyanobacteria (Blue Green algae) often is not even green, but red or to a lesser degree, brown/ red or even orange. These different color variations are due to Phycoerythrin, a red protein from the light-harvesting phycobiliprotein family which is present in Cyanobacteria.

When in free floating form (more common in lakes than aquariums), it will often form a very dense green cloud that may look like paint floating on the water. Some blooms may not affect the appearance of the water. As a Cyanobacterial bloom dies off, the water may smell bad.

Cyanobacteria are from the phylum Cyanophyta of Bacteria that obtain their energy through photosynthesis. They are often still generally referred to as blue-green algae, although they are actually prokaryotes (organisms without a cell nucleus) like bacteria.
Prokaryotes usually are unicellular, although some are capable of forming cell groups called Colonies. Individual Blue-Green Algae that make up these colonies will usually act independent of one another.
Colonies are formed by organisms that remain attached following cell division, often through the help of a secreted slimy layer that we often see as slimy green mat in our aquariums.

Cyanobacteria are the only known group of organisms that are able to reduce nitrogen and carbon in aerobic conditions. The water-oxidizing photosynthesis is accomplished by coupling the activity of photosystem (protein complexes involved in photosynthesis) PS II and I (Z-scheme; the light-dependent reaction, which converts solar energy into chemical energy).
In anaerobic conditions, they are also able to use only PS I — cyclic photophosphorylation — with electron donors other than water (hydrogen sulfide, thiosulphate, or even molecular hydrogen) just like purple photosynthetic bacteria.
Cyanobacteria also have the ability to reduce elemental sulfur by anaerobic respiration in the dark. This is a key point missed by those still promoting the discredited darkening of the aquarium method for control.

A unique aspect of these organisms is that their photosynthetic electron transport shares the same compartment as the components of respiratory electron transport. It is the thylakoid membrane (the site of the light-dependent reactions of photosynthesis) hosts both respiratory and photosynthetic electron transport, while the plasma membrane contains only components of the respiratory chain.

Cyanobacteria, Nitrogen and Ammonia:

Since Cyanobacteria have been around before photosynthesizing plants and before there was any free oxygen in the air, it is thought that Cyanobacteria developed the ability to scavenge nitrogen from the atmospheric dinitrogen gas often dissolved in water. Nitrogen is one of the building blocks of amino acids and necessary to living organisms.
However, even though nitrogen makes up four-fifths of the atmosphere, it is locked away. Cyanobacteria are able to break apart the molecule of dinitrogen and capture the nitrogen gas via Nitrogenase enzymes.

Nitrogenase enzyme molecules are very large, complex enzymes, built of two twisted and balled-up proteins, that combine and recombine to convert a molecule of N2 to two molecules of usable ammonia, NH3. Though Nitrogenase enzymes enable conversion of atmospheric nitrogen so that it can be employed in life processes, it is ineffective in the presence of oxygen. To protect the Nitrogenase from oxygen, many nitrogen-capturing Cyanobacteria (usually of the filamentous variety) have developed special nitrogen-fixing cells called Heterocysts encased in thickened cell walls.
Because of this ability, low nitrate levels are generally not the key to stopping this plague and in fact low nitrates may help cyanobacteria out compete higher plants and algae.

Here is reference site about bacteriolgy that I found both interesting and useful:

Health Risks

Cyanobacteria MAY produce neurotoxins, cytotoxins, endotoxins, and hepatotoxins, all of which are collectively known as cyanotoxins.
The keyword is 'MAY' as this is not the case with all Cyanobacteria, especially many that we find growing in our aquariums.

Specific toxins include, anatoxin-a, anatoxin-as, aplysiatoxin, cyanopeptolin, cylindrospermopsin, domoic acid, nodularin R (from Nodularia), neosaxitoxin, and saxitoxin. Many Cyanobacteria reproduce explosively under certain conditions. This results in algal blooms, which can become harmful to other species, and pose a danger to humans and animals, if the cyanobacteria involved produce these toxins.
Several cases of human poisoning have been documented, but a lack of knowledge prevents an accurate assessment of the risks and ditto as per documentation for dangers to fish in these waters.

As an interesting side note; some studies suggest that significant exposure to high levels of cyanobacteria producing toxins such as BMAA can cause amyotrophic lateral sclerosis (ALS). People living within half a mile of cyanobacterially contaminated lakes have had a 2.3-times greater risk of developing ALS than the rest of the population.

Reference: Wikipedia; Cyanobacteria

TREATMENT (Eradication/ Control);

With some of the above information in hand, one can now make more informed choices about how to eradicate Cyanobacteria.


In saltwater aquariums, Cyanobacteria are often red and appear as a red slime, thus the term “Red Slime Algae” used to describe this in marine aquariums. This NOT to be confused with coralline algae which is indicative of a healthy marine aquarium (see this article about marine chemistry necessary for the growth of coralline algae: “Aquarium Saltwater (marine) Basics”

In Marine Aquariums dissolved organic carbon is the result of anything organic that has died off and gets decomposed by bacteria. Dissolved organics are a food source of the bacterial side of the Cyanobacteria (Red Slime Algae). Sources of this dissolved carbon can include dead algae, bacteria, digested or uneaten food, metabolic waste, and some organic aquarium additives.

Aquarium additives, such as alkalinity controllers, contain bicarbonates. Bicarbonates convert into CO2, thus adding to the carbon levels. This also explains why Cyanobacteria are a common problem in saltwater aquariums.
As with Freshwater, limiting dissolved organic carbon can help, but the bacteria-algae is capable of consuming all the carbon needed derived from CO2. It is therefore important, especially for marine aquariums, to ensure a proper gas-off by water movement and adjustments of water flow.
The more oxygen created, the better the degassing effect.

Filtration such as a well maintained (frequently rinsed) filter can reduce organics and thus carbon. Skimmers are effective tools, but need to be maintained frequently. The Berlin Method that combines mud filtration or a Refugium is also beneficial along with UV Sterilization.

Reference: Aquarium Filtration; Berlin Method

Make sure that if macroalgae, which consume nitrates much faster than phosphates, eliminate all nitrates that this too can open the door to Cyanobacteria.

Further Reading/References:

By Carl Strohmeyer

Other Recommended Reference/Products Sites

Aquarium Light Information, prevention of Blue-Green algae, Cyanobacteria
Aquarium Lighting; Complete Information
Understanding what makes for correct lighting is very important, even for fish only aquariums but even more important for Reef or Planted aquariums!

Hydro Sponge Filter

AAP Hydro Sponge Filters

THE PREMIUM Aquarium Sponge Filter with as much as 5 TIMES the bio and mechanical capacity of commonly sold Chinese knock offs!!
Definitely worth the extra $1-3

Ocean Nutrition Seaweed Salad
San Francisco Bay Brand Seaweed Salad

"Seaweed Salad" is much more nutritious than spinach and lettuce. This product is recommended for all saltwater Damsels, Clownfish, and especially Marine Angels and Tangs

Hydor Smart Wave Controller
Hydor Smart Wave Controller

• Promotes a healthy reef aquarium or similar aquarium environment where wave action is desired by recreating natural currents found in nature
• Synchronous program for currents typical of barrier reefs and alternate for tides

For a friendly, Knowledgeable, aquarium forum with in a family atmosphere:
*Aquarium Forum; Everything Aquatic

Premium Fluidized Sand Bed Bio Filters for Cyanobacteria control
TMC Premium Fluidized Sand Bed Bio Filters

Premium, second to NONE Aquarium Bio Filters, that with Oolitic Sand also maintain essential marine aquarium calcium levels, alkalinity, & electrolytes that are important to ALL Marine life, Goldfish, African Cichlids, Livebearers & more

Non Stop Aquarium Air Pump, AC, DC
Non Stop Air Pump, AC OR DC

This air pump pushes out 4L of air per minute, REGARDLESS of whether you have AC power or NOT


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In Chronological order of writing with the newest at the top

  1. How to Treat Sick Fish
  2. Whirling Disease in Fish
  3. Reef Aquarium Chemistry Maintenance
  4. Use of RO, DI, Softwater in Aquariums
  5. Lighting Theory of a Planted Aquarium- RQE, PFY, PAS, & PUR
  6. Aquarium or Pond Bio Load
  7. Tuberculosis in Fish
  8. PUR vs PAR in Aquarium Lighting
  9. Head Pressure in Aquarium and Pond Water Pumps
  10. Fin/Tail Rot For Betta & ALL Fish
  11. Angelfish Virus/Aids
  12. Activated Carbon
  13. Fish Baths/Dips as an aid to treatment
  14. Streptococcus gram positive bacterium in aquariums, Eye Infections
  15. Hydrogen Sulfide
    production in anaerobic De-Nitrification for Aquarium/Ponds
  16. Fish Shipping
  17. Aquarium Size, Fish Stunting
  18. Aquarium Algae,
    BBA & Brown Algae in particular
  19. Aquarium Salt (Sodium chloride) in Freshwater Aquariums
  20. Betta Habitat; Wild Bettas to Domestic Betta environment parameters
  21. HITH; Hole in the Head Disease
  22. Aquarium Protein Skimmers, Ozonizers
  23. Power Head/ Water Pump Review
  24. Molly Disease/ Mollies in an Aquarium
  25. Basic Fish Anatomy, Fin Identification
  26. Aquarium Moving/ Power Failures
  27. Octopus as Aquarium Pets
  28. Aquarium Nitrates
  29. Ichthyophonus protists, fungus in fish
  30. Aquarium and Pond Filter Media
    Types; Mechanical, Bio, Chemical
  31. Aquarium Water Conditioners (also Pond)
  32. Fish Parasites; Trematodes & Monogeneans; Annelids and Nematodes;
    Flukes, internal worms, Detritus Worms (often confused with Planaria), Micro Worms
  33. Aquarium Silicone Application;
    DIY Aquarium Repair & Glass thickness
  34. Pond Veggie Filters; DIY Bog Filter
  35. The difference between Plaster of Paris and Aquarium Products such a Wonder Shells:
    Identification, prevention & Treatment
  37. AQUARIUM TEST KITS; Use & Importance
  38. SEXING FISH; Basics
  39. Chocolate Chip, Knobby and Fromia Starfish
  40. Freshwater Velvet & Costia
  41. Usnic Acid as a Fish Remedy
  42. Aquarium Heaters; Types, information
  43. The Lateral Line in Fish, Lateral Line Disease
    or Head and Lateral Line Erosion (HLLE)
  44. Tap Water use in Aquarium; Chloramines, Chlorine
  45. Can Black Ghost Knife fish give an electric shock?
  46. Bio Wheel Review; Do Bio-Wheels really work?
  47. How do Fish Drink?
    Use of RO Water
  48. Cyclops, and Predatory Damselfly larvae
  49. Betta with Dropsy;
    Treatment and Prevention of DROPSY in all fish
  50. pH and KH problems in African Cichlid Aquarium
  51. Aquarium Gravel, which size?
  52. Blue green algae, Cyanobacteria in Ponds/Aquariums

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*Sponge Filters that far outperform all other brands or DIY:
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