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Dosing 3% hydrogen peroxide to an aquarium has been reported as an affective treatment for green hair algae (GHA). Applying it at a rate of 1 mL per 10 gallons, or about 1 ppm, GHA is supposed to die within days. I wondered if this were true because hydrogen peroxide is not stable in an aquarium.
My first test was a “let’s see what happens” type of experiment. In one test, I dosed hydrogen peroxide to a petri dish which contained a mass of growing GHA in 12 mL of medium. A second experiment involved a similar amount of GHA in a petri dish, but this time the dish was submerged in 100 mL of medium. The point of this second experiment was to expose the GHA to much more hydrogen peroxide before it decomposed. Each experiment was dosed daily for six days. The plots below shows how long the hydrogen peroxide lasted after dosing in each experiment. The 12 mL test roughly exposes GHA for a time similar to that in an aquarium. A visual and microscopic examination on day 7 revealed no apparent effect.
The next experiment included controls and also tested whether a low nitrate level (10 ppm v 100 ppm) might enhance the effect of H2O2. The cultures were actively growing in 30 mL of medium. This gave an exposure time between the extremes in first experiments. The culture was dosed daily for six days and examined on day 7. No difference was noted between the controls and tests at high and low nitrate levels.
The final test used a GHA culture similar to the one used in the first experiment, but submerged in 1 L of medium to dramatically increase the the exposure time to hydrogen peroxide. The plot below shows the hydrogen peroxide concentration after a daily dose. Unlike the previous experiments, hydrogen peroxide was present throughout the day. The experiment was dosed daily for five days. The before and after photographs below provide no visual evidence of an effect on day 6.
BEFORE
AFTER
Why does hydrogen peroxide appear to be an ineffective GHA treatment?
I found numerous scientific papers demonstrating hydrogen peroxide’s deleterious effects on freshwater and marine organisms at or below 1 ppm. Two conditions seem to be important for this effect. The organism has to be susceptible to hydrogen peroxide poisoning and the concentration must be sufficiently high. GHA (or organisms growing on the filaments) seems more than capable destroying hydrogen peroxide, keeping it at very low concentrations. It also seems to be able to keep hydrogen peroxide from entering its filaments even when it cannot completely destroy it. A more careful look might reveal some level of stress experienced by GHA exposed to hydrogen peroxide, but it does not seem to qualify as an algicide.
By the way, these GHA cultures aren't off the hook yet. They are now being exposed to Vibrant.
My first test was a “let’s see what happens” type of experiment. In one test, I dosed hydrogen peroxide to a petri dish which contained a mass of growing GHA in 12 mL of medium. A second experiment involved a similar amount of GHA in a petri dish, but this time the dish was submerged in 100 mL of medium. The point of this second experiment was to expose the GHA to much more hydrogen peroxide before it decomposed. Each experiment was dosed daily for six days. The plots below shows how long the hydrogen peroxide lasted after dosing in each experiment. The 12 mL test roughly exposes GHA for a time similar to that in an aquarium. A visual and microscopic examination on day 7 revealed no apparent effect.
The next experiment included controls and also tested whether a low nitrate level (10 ppm v 100 ppm) might enhance the effect of H2O2. The cultures were actively growing in 30 mL of medium. This gave an exposure time between the extremes in first experiments. The culture was dosed daily for six days and examined on day 7. No difference was noted between the controls and tests at high and low nitrate levels.
The final test used a GHA culture similar to the one used in the first experiment, but submerged in 1 L of medium to dramatically increase the the exposure time to hydrogen peroxide. The plot below shows the hydrogen peroxide concentration after a daily dose. Unlike the previous experiments, hydrogen peroxide was present throughout the day. The experiment was dosed daily for five days. The before and after photographs below provide no visual evidence of an effect on day 6.
BEFORE
AFTER
Why does hydrogen peroxide appear to be an ineffective GHA treatment?
I found numerous scientific papers demonstrating hydrogen peroxide’s deleterious effects on freshwater and marine organisms at or below 1 ppm. Two conditions seem to be important for this effect. The organism has to be susceptible to hydrogen peroxide poisoning and the concentration must be sufficiently high. GHA (or organisms growing on the filaments) seems more than capable destroying hydrogen peroxide, keeping it at very low concentrations. It also seems to be able to keep hydrogen peroxide from entering its filaments even when it cannot completely destroy it. A more careful look might reveal some level of stress experienced by GHA exposed to hydrogen peroxide, but it does not seem to qualify as an algicide.
By the way, these GHA cultures aren't off the hook yet. They are now being exposed to Vibrant.