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Hi The Big Buddha,

When I have an outbreak of Cyano I typically start with dosing hydrogen peroxide (H2O2) - the 'standard' 3% concentration found in drugstores and grocery stores.

Before a treatment I make sure that my lights have been on for at least 20 minutes so the plants (and especially the cyano) are at full photosynthesis, that seems to maximize the oxidation that occurs when the H2O2 contacts the algae (actually cyanobacteria has both plant and bacteria properties). Also before treatment I turn off all pumps, filters, and airstones that cause currents in the tank allowing the water to become still. Then I use an oral syringe (about 10cc; also available at your drug store), fill it with the H2O2 and "paint" areas where the cyano is most dense. How much do I dose? I dose a maximum of 1.5 ml per gallon per 24 hours. If dosing a 10 gallon tank I use a maximum of 15 ml per treatment (1-1/2 syringes), one treatment per 24 hours. If dosing a 20 gallon I dose a total of 30 ml (3 syringes) per 24 hours. After about 5 minutes I see bubbles being released in the treated area(s) which tells me the oxidation of the cyano is occurring. When the bubbles have stopped, usually about 15 minutes after treatment, I turn on all filters and pumps. Keep in mind that although the water is "still" you may see bubbling in areas not treated directly treated because the H2O2 has drifted on currents caused by moving my hand in the tank. Usually one treatment per area is all that is required. Why does hydrogen peroxide seem to work so well? Since H2O2 is an oxidizing agent it attacks the chlorophyll (the plant portion) of the Cyano and H2O2 also kills bacteria (the other characteristic of Cyano).

I have used this treatment many times over the years and have always found it effective and have not harmed any fish (Cardinals, Apistos, Corydoras) nor has there been any evidence of harm to beneficial bacteria in my filters. If I have an Cyano outbreak it seems to be a result of either low nitrate levels, poor water circulation, or a filter that needs to be cleaned.
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