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Hydrogen peroxide (H2O2) is a weak acid that has strong oxidizing properties. In its pure form, it is a pale blue liquid slightly more viscous than water, but when diluted, it appears colorless.
Genreally, it is used as an oxidizer, bleaching agent, and antiseptic.
Hydrogen peroxide can be found in different forms from 1-90% H2O2.
You should be careful when using it because at concentrations higher than 20%, it can be corrosive and harmful to your hands.
Although a potent and somewhat toxic chemical, it can be used in aquariums in low dosages and with great care to kill algae and as a treatment for marine fish.
Even so, I still get questions regarding Hydrogen peroxide use in freshwater fish tanks.
For instance, will hydrogen peroxide kill your tropical fish?
Well, when used in the correct concentrations and proportions, hydrogen peroxide will not kill healthy fish.
The problem comes in when you use H2O2 that has a high concentration….
…then, it will inevitably kill your fish.
Many people use Hydrogen Peroxide in their freshwater aquariums as an algaecidal, for spot treatment on occasion, and plant dips with no ill effect, but care should always be taken.
The recommended concentration for use in fish tanks is 0-3% H2O2 solution.
In fish tanks, hydrogen peroxide can be used as an algae killer, an antibacterial agent, and also as an oxidizing agent.
See more insight below.
What Does Hydrogen Peroxide Do To Fish
Hydrogen peroxide is a chemical compound comprised of water and an extra oxygen molecule.
When added to water, it breaks down into water and oxygen.
Therefore, it can be used as a source of extra oxygen for aquarium fish.
But on the other hand, when a high concentration of hydrogen peroxide is used in aquariums, it may cause retarded growth and destroy the fish gills leading to your fish’s death.
Some plant species like coral moss and liverwort may also be damaged by hydrogen peroxide.
As such, when adding H2O2 to your aquarium, please consider these facts.
Hydogen peroxide is also used for spot treatment in ornamental aquarium fish.
The treatment helps knock off flukes, protozoans, fungus, and bacteria in the gills and body of our beautiful finny buddies.
That said, when using this treatment, you need to be extra careful and read the researched instructions carefully because it can have effects on your fish.
How Do You Treat an Aquarium with Hydrogen Peroxide
Hydrogen peroxide, in the correct concentration, has many uses in an aquarium.
At some point, your aquarium may be infested with the stubborn green algae or the blue-green algae that doesn’t come off no matter how much you try and sometimes becomes very ugly.
Hydrogen peroxide comes in handy when you want to remove these algae from your tank.
Ordinarily, the recommended concentration is 1ml H2O2 per one gallon of water…
…but we have different dosages when treating the blue-green algae and the green algae using hydrogen peroxide concentration.
In the case of blue-green algae, the recommended dosage is 8-15ml of the 3% solution H2O2 per 50 liters of water.
For the green algae, the recommended dosage is 25 -35 ml of 3 percent hydrogen peroxide and 50 percent water solution.
Below is a source of more information on how to calculate the dosage to use while treating the algae in the aquarium
Also used for spot treating stubborn algae such as black beard when you don’t want to add H2O2 to your whole tank.
The best tool to use in this case is a syringe.
Suck a little hydrogen peroxide into a syringe and use it to apply on the surface of the plants or parts of the aquarium infested with algae.
You will notice bubbles coming from the surface once the algae start breaking down.
Leave it for a few minutes and clean up the plant.
Since hydrogen peroxide also kills the beneficial bacterial in the aquarium, a water change of at least 50% in the tank is recommended.
Hydrogen peroxide is also used for tank sterilization in instances of diseases or bad algae infestation.
Here, the tank is filled with water and, the whole system runs for 24 hours.
After 24 hours, the tank should be emptied and run again for another 24 hours, and at this point, you are sure the tank is safe and ready to be in use all over again .
It also comes in handy when cleaning and sterilizing horse pipes, and fishnets used in aquariums.
How Much Hydrogen Peroxide for Fish
As we have already discussed, hydrogen peroxide is a chemical compound that is highly reactive and acts as an oxidizing and bleaching agent.
Because of these properties, it has many medical and non-medical uses.
Since it’s highly effective, it is used in aquariums against numerous external fish disease-causing organisms.
But always keep in mind that a high concentration of hydrogen peroxide is toxic and can be harmful to our fishes in the aquarium, we need to know and be sure the amount of hydrogen peroxide solution ideal for our aquariums.
The fish species and the concentration is also a major determinant of its toxicity to fish.
The best hydrogen peroxide solution for fish is 0-3% solution.
This hydrogen peroxide percentage solution will neither be toxic to your finny buddies nor will it affect their gills.
Moreso, it will not cause any stress to the fish in the aquarium.
A point to note
One last point to note is, hydrogen peroxide can be harmful to your aquatic plants and the fish in the tank, so always read the safety instructions before use.
When using this chemical, wear protective gear and avoid direct contact with skin, eyes, and clothing.
Moreover, unless you are doing a fish bath with the correct recommendations, make sure hydrogen peroxide does not come into contact with your finnies or plants.
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Happy Fish🐡🐟🐠 Keeping.