Cyanbacteria is just that a bacteria and not truly a form of algae. There are several ethods of getting rid of cyano as well as there are several causes.
First we can start with the treatments.
Organics
I would avoid the introduction of biological animal to treat the bacteria. You can and may want to increase your cleanup crew, but there is a reson they died in the first place that needs to be addressed. While sand sifting stars will sift your sand for you, they also rob your sand bed of the fauna that grows there, greatly diminshing the sandbeds ability to filter the water. Also most sand sifting star fish starve in home aquariums that are not properly established, I would not consider a 7 month tank established. Cycled hopefully yes, but not established.
While avoiding the introduction of animals there are several other biological ways to help control the excessive nutrients in a system. Macro alages are great at out competing nuissance algaes for nutrients and will provide overall better water quaility. IMO these are best housed in a refugium seperate from the tank where they can be lit 24/7 to avoid going sexual which will cause then to disinegrate and fowl the water. I do keep prolifera and red grape caulphera in my display systems, but leave the suction cup caulphera and the green grape caulphera as well as chaetomorpha in the refugium. IMO chaeto is fine housed in a display, but it doesn't meet my "awe" factor for being housed in my display. IME while macro algaes are great for systems, and will help control nuissance algae, once an outbreak occurs the nuissance algaes or bacteria will cover the macros the same they will a piece of LR.
chemical
There are chemical treatments such as chem clean that can be added directly to the system. Most of these treatments require you to turn off your filter for the duration of the treatment and many require 20% or larger water changes after the cycle of the treatment is completed.
When I first ran into this problem some years ago I was very leary about putting anything non natural into my systems. After severe battles I decided to give them a try. Chem Clean worked well for me at first, but after time passed I found myself having to increase the dosages, and frequency of doses to combat the same problem. It is my belief that the chemiclas kill the weakest cells, and leave the strongest cells to multiply and cause a larger problem down the line. JMO
There are other chemicals such as phos ban that can be placed into a cannister filter for long term phosphate reduction in the system. These products will last around 90 days IME and then need to be replaced.
filters
There are many ways to filter out the excessive nutrients in your system that are one of the major factors in the cause of cyano bacteria. Any type of filter with a poly pad will be effective at catching the pieces of phosphate so they can mannual be removed.
Cannister filters are great IMO because they have the compartments that you can customize to your tanks needs. (see chemicals above, reference phos ban)
UV Sterilizers are effective if run at a low enough flow of killing the bacteria and algae that passes through them by exposing them to a UV light. To get the most out of your UV run it at the lowest gph setting suitable for the sleeve, and make sure it is inline after a water polishing device so no bacteria is able to hide on a piece of detrious as it passes across the sleeve.
Protien skimmers are effective at removing extra nutrients and DOC's from the water column. These are one of the more popular hobbyist choices.
Ozone filters clean water removing organic decay, protein and pollutants by passing oxygen molecules over a special light source. these will also help rid your system of nutrients.
Refugiums both hang on and sump style models are great at providing a place for the more natural types of filtration. I am a big fan of the Eco System models, but they are pricey. YOu could also go with a CPR style HOB and use the Mineral Mud from Eco System. JMO
You could also utalize a phos reactor. They can be combined with different styles of media but there primary purpose is to eliminate phosphates.
Easy but Effective
I have tried most of the things listed here. Still I have found the easiest and most effective way IME is to turn off the aquarium lights for 48 hours continously. Just keep um off,the fish and corals will all be fine. The cyanobacteria is photsynthetic. Removed from a light source it will die. The great thing about this is all of it will die and you will only have repeat occurances if there is a source problem in your system.
Other things to do
Add an Airstone. Increased oxygen in the water will help to kill cyano
Check you PH, nuissance algaes favor low PH IME
Common Causes
The most common cause of cyanobacteria is excessive nutrients in a system. If you are over feeding your corals or your fish, this is a problem that is easy to remedy, stop feeding so much. Your corals and fish both have a set limit on what they are able to consume in a day. There is no point exceeding it.
If you have corals that are filter feeders instead of dosing the entire system, you can easily target feed that coral. This is done by placing the esired food in a syringe or turkey baster and gently squirting some food towards the coral.
If there is any uneaten food, suck it back out of the system, and next time, feed less.
Another common cause of cyanobacteria and nuissance alage is low flow. Tanks with lower flow can be prone to "dead spots" between there rocks. This is an area where detrious is able to settled and acumulate over a span of time. This will be a breeding ground for problems.
Different species of fish and corals have different needs in regards to flow. If your keeping seahorses, your flow of your tank will need to be between 3x to 5x the volume of the tank turned over per hour. If your keeping more traditional fish, rule of thumb is around 20x an hour. It is good to know what the needs of the fish or corals you are keeping are, and adjust your tank accordingly.
If you have lots of rock work, you may consider putting in a PVC structure that can act not only as a support for the LR aquascaping, but also as a spray bar if you drill in some holes and attach a pump. Since doingthis in my systems, I have had no issues with cyano or nuissance algaes, and I feed my system quite a bit.
Aging light bulbs will also contribute to the growth of cyano bacteria and nuissance algae. Aquarium lightbulbs have a listed life span, not because they will no longer work after a certain date, but because of continual usage the light spectrum the light emits begins to shift to more of a red spectrum which is a favorite of the cyanobacteria and many nuissance algaes.
Hope it Helps.
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