Treatment:
The first step should be a mechanical removal as much of the cyanobacteria as possible. It's important, however, to pay attention to not spreading the cyanobacteria around the aquarium when we will be removing it. The best way is to wipe it out with a toothbrush (used exclusively for cleaning the aquarium), and at the same time suck the wiped pieces of cyanobacteria using a vacuum cleaner. The next step in the fight against cyanobacteria should be regular and frequent water changes (sometimes it's advised to use rather demineralized water due to the low nutrient content). It may follow 3-5 day blackout of aquarium (e.g. black wrapping paper or black quarters), or limitation of the photoperiod → it is, however, necessary to proceed with caution here, because if during the blackout dies suddenly more cyanobacteria, it may result very quickly in contamination of your aquarium by toxic substances, which can have disastrous effects (during the blackout it's therefore important to carefully monitor the aquarium, often change the water and vacuum/remove organic waste, frequently clean the filters, and ensure good circulation and better oxygenation of the water). In some cases, the blackout need not help. Moreover, we should focus on improving water circulation for better gas exchange (=> increase of concentration of dissolved oxygen in the water). Oxygen apparently suppresses the growth of cyanobacteria. On the contrary, in waters poor in oxygen the cyanobacteria thrive. A number of studies have reported the blooms of cyanobacteria in relation to the deterioration of water quality, mainly due to increased levels of organic compounds, in which several factors plays role: for example, the decay of the substrate, too much food, too little water changes, or nutrients overloading. Aquarists tend to have a good experience also with directing the outlet of the filter with oxygenated water directly to the affected area. To destroy cells of cyanobacteria you can also use hydrogen peroxide (H2O2) or permanganate (KMnO4), both of which act as oxidizing agents. Peroxide (2H2O2) in contact with the light breaks into 2H2O + O2 (oxygen and water), which immediately kill cyanobacteria within a few minutes (if you dose it locally to the most affected areas). The recommended dose of peroxide should not exceed 1 ml per 20L of water (preferably dosed every 30-60 minutes). Too large doses, however, could also damage the nitrifying bacteria (which is why it is good to be careful with their use). Starvation does not work very well with cyanobacteria (like with all other algae), because a significant reduction of nutrients will hurt especially plants (and thus it's useful only in tanks without plants). The increase of CO2 and some nutrients (mainly nitrates) allegedly helps against cyanobacteria. Although not yet revealed exactly why this works, it could to some extent be related to the improvement of plant growth. The best thing in the fight against cyanobacteria (as with all other algae) seems to be the deployment of large numbers of healthy and thriving plants (ideally we should plant 70-80% of the bottom surface), which (among other things) maintain the low level of nutrients, and on the contrary a high level of dissolved oxygen in water also, which may have a negative effect on unprotected cell walls of cyanobacteria (which can survive in this environment only if they wraps themselves in a thick layer of biofilm or diatoms). I also recommend to use a reasonable thickness of the substrate (not too thick), because the nitrifying bacteria will thrive best in the substrate with a thickness of up to 2 inches (if the thickness of the substrate being larger there may begin to predominate rather de-nitrification processes in the substrate). It is equally important to provide sufficient time for the propagation of a sufficient amount of useful bacteria in newly established aquariums, and give them at least 60 days before the tank will accomodate the first animals (fish, shrimps). Furthermore, it is good to add the fish gradually to the tank, so that the beneficial bacteria could multiply sufficiently, and completely cover the increased accumulation of waste. Similarly, it is also good to maintain a proper alkalinity (ideally around 6�dKH) and pH (preferably neutral or slightly alkaline pH → 7-8). Although slightly acidic pH affects negatively the majority of cyanobacteria, it is important to remember that just as negatively it influences the nitrifying bacteria. So when you can not avoid the slightly acidic pH (around 6.5), then we should compensate it by significantly reducing the number of fish in the tank = production of waste materials (preferably at least by 50%). As the cyanobacteria belong to bacteria (not algae), it is possible to use also antibiotics as a last resort (including erythromycin). However, it is important to remember that "the aquarium is an ecosystem, which does not react too well to antibiotics and toxins" (Diana Walstad). It is appropriate to remember also that during mass die off of cyanobacteria due to the use of antibiotics they may release a large amount of toxins (and sometimes to produce larger quantities of ammonia) that can stress the fish and other animals in the aquarium, and in some cases they may even be fatal to them. Despite all this the use of antibiotics may be in many cases inevitable and the only effective solution.
