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By Lisa Harmison
As some of you may recall, at a meeting earlier this fall the topic of algae control came up. Someone shared his experience of using hydrogen peroxide in his container water garden with great success. He also shared where he found some information on the internet (Garden Web forum, http://faq.gardenweb.com/faq/lists/ponds/2002051559024333.html).
Well, I started looking into this and here is what I found so far.
The Garden Web forum has a lot of information about all things gardening. I looked into the hydrogen peroxide as algaecide and read several threads there. I also did a search on hydrogen peroxide and algae. Lots of interesting hits there too. I also investigated hydrogen peroxide only websites. (Ok, I like to surf the web.)
Hydrogen peroxide consists of two hydrogen molecules and two oxygen molecules (H2O2). It is a very common compound, found in our bodies as well as in nature. It is a relatively unstable molecule, primarily an oxidative reaction occurs to remove on of the oxygen molecules (resulting in water). It can be used as a disinfectant, antiseptic, cleaner, and whitener, just to mention a few of its uses. Hydrogen peroxide also comes in various concentrations for its uses; the most common is the 3% solution found in the bottles in drug stores. A 35% solution is being used by municipal water treatment facilities instead of chlorine. Higher concentrations are more dangerous.
Hydrogen peroxide is used by hydroponics growers to maintain the health of the plants they grow (http://www.quickgrow.com/gardening_articles/hydrogen_peroxide_horticulture.html). Hot tub owners can use it instead of chlorine to cut algae. It can also be used to rid fish tanks of algae. Keep in mind though, that what I found for fish tanks and ponds is mainly anecdotal evidence. No scientific experiments were found anywhere on-line.
The scientist in me wants the controlled experimental evidence. The curiosity in me wants to know what the hydrogen peroxide does to the algae and to other organisms (plant and animal) in the water. So I did a little experiment. I have a fish tank that I let get a bit green. I put in some peroxide (2 oz. of 3% solution per 10 gallons of tank water). Nothing has changed after three days. Now I didn't spot treat the algae as was described at one website (http://www.thekrib.com/Plants/Algae/hydrogen-peroxide.html). Also, I don't know for sure if I have what species of algae I have - string or blue-green algae or what. My fish (three regular goldfish and one sword-tail goldfish) and plants (Elodea) do not appear to be hurt. I looked for microscopic organisms but could not find any before the treatment so I do not know what affect the peroxide would have on them.
My next experiment will be more controlled. I plan to isolate some string algae and see what happens when treated with peroxide. I also plan on finding some microorganisms (Daphnia, paramecium, etc.) and see what happens to them when exposed to peroxide. I may test a few other things I haven't thought of yet. I'll let you know what I find.
The evidence so far seems to indicate that the hydrogen peroxide doesn't necessarily kill what is already present but prohibits new algae growth, especially string algae. This comes from what I found in regards to how barley straw works in ponds ( http://www.aquaart.com/BarleyStraw..html and the handout from Dr. Joe Morris last year, also on our website under Puddle Jumping). (I sent Dr. Morris an e-mail note but he hasn't responded). Hydrogen peroxide is one of the by-products of the decomposition of the barley straw. The straw does not work on reducing the string algae already present (that's why it is recommended that you remove as much as you can before putting the barley straw in your pond). There is some evidence that the barley straw provides a low, constant level of H2O2 in the water that inhibits new string algae growth.
In all I researched, there are also reports that the barley straw and/or the hydrogen peroxide treatments do not work at removing algae. My conclusion is, if you wish to try it, do so with a very low concentration of hydrogen peroxide. If you are concerned about your fish, plants, snails, or other critters, remove them before treating. Also, if you try it, let me know what you did and what your results were. I'll keep you posted.