Dosing Peroxide (H2O2) is an other interesting way to control/kill algae. Dosing Peroxide has proven to be very effective against Cyanobacteria, Black Brush Algae and Green Hair Algae but like any quick fix, this method won’t solve the root cause of algae in your aquarium. I recommend dosing Peroxide in conjunction with steps to get at the root cause: nutrient imbalance, light, etc.
Why Peroxide?
Peroxide is caustic (not toxic) which mean that it is able to burn or corrode organic tissue by chemical action. According to what I found online (see WaterScapeNorthwest.com, Peroxide has also been scientifically proven to reduce the capability of algae to form new cell growth. Peroxide also rise the O2 level which some algae (like cyanobacteria) hate very much.
How Much Peroxide Is Safe
I have been looking around the Internet trying to find a general dosing rule. I have found many posts where people claim to use 0.5ml to 2ml per gallon of 3% Peroxide in tanks with fish and shrimp without any problem. I also found many posts where people claim to use as much as 3ml of 3% Peroxide per gallon. Most say they perform a 25% water change 30 min after dosing peroxide.
Overdosing peroxide can kill so I try to use it VERY conservatively! As Tom Bar was saying on The Barr Report, “besides gassing fish with too much CO2, Peroxide seems to kill the most, followed by Excel overdosing”. Seen this way, I will certainly not be one of those who dose 2 or 3ml per gallon. Actually, I am way more conservative than that and only dose 0.2ml per gallon every 4 hours! I don’t see the need for more. It is enough to treat small patches of algae at the time and I don’t have to freak about killing fish or inverts. I have been dosing 0.2ml per gallon every 4 hours in both fresh and saltwater aquarium without problem and it is very effective. I never had to do a water change after dosing Peroxide. The only precaution I take is to not dose Peroxide near my corals and anemones when treating my reef tank.
Using Peroxide
The best way to use Peroxide for algae control is to spot treat a small patch of algae with a syringe. Spot treating with Peroxide takes some time but it is very effective. To spot treat, turn your filter off to stop water flow, and inject some Peroxide directly onto the algae you want to kill using a syringe. You are free to use as much Peroxide as you want but I strongly recommend you to not use more than 3ml per gallons and to proceed to a 25% water change 30 min after. If you want to stay on the safe side, 0.2 to 1ml per gallon is perfect. As said previously, I get good results with 0.2 ml per gallon so why use more and run the chance to kill the aquarium inhabitants.
This week I am trying to treat some live rock outside of my display tank hoping this could be a good way to clean the rocks of hair algae without risk. I will post the results here once I am finish with this experiment. Basically, I move the rock outside the tank and spray Peroxide on it. After 15-20 min, I rinse the rock and move it to a quarantine tank and wait for results. To be continued…
One last thing: Only use a fresh bottle of Peroxide (H2O2). Buy smaller bottles at a time, say 2-4 oz, this way you always have a relatively fresh bottle on hand. Peroxide goes flat over time.
Conclusion
Peroxide is a great help in killing unwanted algae. It allows to do it without all the work involved in using bleach or side effects of most copper based algaecides and similar products. Peroxide is also very cheap!
Source: Aquariumslife.com
