Fighting the algae with Hydrogen Peroxide - ΙΙ

by George J. Reclos

After 24 hours the black algae had become pink algae. Although really impressive, still the algae was there. Was it dead ? Then why was it still attached to the plants ? Since there was nothing more I could do I decided to wait for one more day and then ... decide which the next step would be.

The black algae has turned to light pink. Definitely some kind of damage was done. What remained to be seen was whether it would still survive.

My filter's outlet dressed in pink.

Twenty four hours later (48 hours after the addition of the hydrogen peroxide solution) the pink algae was mostly gone. Some traces remained in some places but those big hairy balls were not there anymore.

Even the filter outlet is now clear of it. Well, this was a fantastic result, an 100% successful intervention. Or wasn't it ?

As anticipated, plants didn't tolerate the presence of hydrogen peroxide well. Of course, plant cells and algal cells share many things so, something so devastating for the black algae would definitely harm the leaves of my plants in some way. Of course, even if one third of the plants survived still I would be happy. We all know the other alternative: get rid of all the plants, empty the tank etc.. Not for me, if I can avoid it. The photo above shows the tank immediately after the application of the peroxide.

The leaf of Echinodorus ozelot 4 days after the addition of hydrogen peroxide. As you can see, all soft tissue is severely damaged. Well, you can't win them all, can you ? If I were to classify my plants according to their resistance to hydrogen peroxide I would make three lists. Those which were not affected: Microsorium pteropus, all Cryptocorines, Rotala rotundifolia and all Anubias. Those which lost many (even too many) leaves but new leaves are normal and the plants look absolutely healthy now: Ricia fluitans, Echinodorus ozelot, Nymphaea lotus and Hygrophila corymbosa. Finally, hornwort was practically as dead as the black algae. However, even removing it before the application of the peroxide is not an option since its re-introduction would bring the algae back in the tank.

This photo shows the tank after 4 days. Many plants had to be cut back, many leaves to be removed, some plants didn't even make it at all. However, in the end, far more than one third of the plants survived and - with the exception of hornwort - all other plants have produced new leaves with normal soft tissues. Asked if I would do it again, the answer is "definitely yes". I don't know if adding the hydrogen peroxide in the water column and letting it to dissolve slowly would be equally beneficial or less hard for the plants. Frankly, I hope I will never find out - not in my tanks anyway. The main issue is that I enriched my arsenal with one more - very effective - chemical directed against one of the most persisting types of algae. So do you.


Another hobbyist, Bill Zdarko from  Fort Myers, Florida, USA, gave this method a try and here is the information he would like to share with other hobbyists:

Bill: I added some hydrogen peroxide to my fish tank to remove some black algae. The problem was I did not know how much to add.  I turned the filter and air off to stop the current in the tank.  I put in about 60-70cc in a 20 gallon tank with a 20cc syringe injected directly on the black algae. Waited about 5 min and started the air and filter.  With that I lost about 1/3 of my fish but the plants look better. Could you go in detail on how much H2O2 to add to a gallon of water when treating for black algae.  Iím guessing that 1cc per gallon would be the limit, I put in about 3cc per gallon, thatís way too much for the fish. Of the fish that died, 2 algae eaters, one cat fish, a silver hatchet fish and one neon that is  still MIA.  Seems the bottom feeders were effected more. I added H2O2 at night, knowing that the hydrogen peroxide breaks down quickly in light.  To me this would make a greater effect on the black algae and unbeknownst to me, the fish.  Its only been 12+ hours since I added the H2O2 so I may loose more fish.  As for the black algae, it looks a light green now. Perhaps another fish tank enthusiastic can learn from my mistakes.

George: In my article I mention 3x60 ml injections (180 ml in total) of a 3% hydrogen peroxide solution for a 240 litre tank (which means 0.75 cc of a 3% solution / litre = 2.8 cc pf a 3% solution / gallon). In short, if you were using a 3% solution, the dosage was correct. However, I think that the "mistake" was that you stopped the filters. I would perhaps stop the aeration but not the filters since I wanted the H2O2 to go everywhere and not have areas with a high concentration of it since it will burn the gills of the fish on the spot (this is how it acts on algae, too). Furthermore, as I said in that article, you have to add it slowly. I added those 180 ml over a period of 5 minutes.. Please let me know what happened.

Bill: My tank would be a 80L tank, take in the consideration of sand, gravel and rocks then I have about a 70L tank.  I added about 60-70ml of H2O2 of a 3% concentration.  That gives me a ratio of about one ml per litre of water.  I added slightly more than what you added, (3ml of 3% / gallon).  I think this might be the mistake. I added the H2O2 over about 5 minutes and I only stopped the filter and air for that amount of time.  Soon as I was done adding the peroxide I started the system up again. After you added your H2O2 did you leave the lights on?  I know that peroxide is extremely unstable in light, thatís why its packaged in non-clear containers.  My lights went off about 1/2 hour after I added the H2O2.  Iím wondering if that kept a higher concentration for too long in the tank. Also 1/2 of the fish that died were bottom feeders and the neon that died was only about 2 cm long, very small fish. Like I said before, the black algae is gone and most of my plants seem to be fine.  I might have to trim back the pearl grass.  If I ever get black algae again I would like to do this treatment again but with fewer fatalities. One think I would like to add is that my ammonia level is up slightly after adding the H2O2.  Iím guessing my bacteria count is really out of wack now.

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