peroxide for algae control; finally figured it out!

hollyhockdoll(z5 IN)October 24, 2010


Hey everyone,

I haven't posted for a very long time (life gets in the way, etc.) but there was a discussion a couple of years ago about using peroxide in the pond for algae control, but there didn't seem to be a lot of information and/or conclusive evidence one way or the other. Well, I spent the last two summers messing around with this whole peroxide thing, and I think I've finally got it down, so I thought I'd share what I've learned, because the results kinda surprised me.

My pond is (I think) 4 years old, about 1200 gallons, about 30" at its deepest point, and the liner is covered with rocks and pea gravel. I have a skimmer that pumps water to a "skippy" type filter filled with watercress, WH, WL, etc. There are about 10 goldfish of various sizes, and one beautiful 10" butterfly koi (Sunny) in it. I always felt that the pond was very easy to maintain, except for the string algae! My pond is in full sun, and because I am zone 5, it takes awhile for the plants to provide enough filtering and leaf cover to keep the algae at bay. In the meantime, the algae would drive me insane. I do things as naturally and organically as is feasible for me, so I DID NOT want to dump a bunch of chemicals in the pond. Nor did I want the pond to be completely algae free (it is a vital part of the ecosystem, after all). So last summer I decided to find out once and for all if peroxide is a viable alternative for algae control. That summer, by trial and error, I figured out the proper "dosage", and learned that it really does work. This summer, I refined my dosing schedule and determined that it DOES NOT mess up the spring "cycling" (peroxide does not seem to affect single cell algae as much as string algae). So, here is my plan for using peroxide to control algae:

* First, determine how much peroxide you need. I am guessing at my pond's 1200 gallon capacity as it is irregular in shape and depth, and there are quite a few large rocks in it, so I can't really get accurate. But I have learned that it takes 5 quart-sized bottles of peroxide (the large ones at Walmart - about $1 each) to control the algae in it. If you do the math, that's one quart for about 240 gallons, but you want to start with less, then keep adding more each time until you can see that the algae is dying. I started with 3, which did NOTHING. Then went to 4, which did NOTHING. Five did the trick.

* After opening the pond up in the spring, I put in 5 quarts of peroxide, because the string algae had already started. The pond cycled as usual, turning green, then clearing. The peroxide did not affect this process. This first dose did not kill the string algae (guessing because it was cool), but it did stunt its growth. I just poured the peroxide in straight from the bottle in 5 different places (I poured one in the skippy filter), but my pond is large enough & the pump powerful enough that I didn't have to worry about my fish - in a small pond you would want to dilute it with water first.

* I kept an eye on the algae growth after the pond cycled. When the weather warmed up, I would put 5 quarts of peroxide in every two weeks. I had to do this through May, June, and half of July. As long as I kept up that schedule, the string algae never got out of hand. It would be a 1" "fuzz" of algae on the rocks, and, within a day or two of treatment, it would turn brown. In another day, it would be filtered away (and, as a side note, the plants in my skippy did better than ever!), leaving that barest film of algae on everything that just makes the pond look more natural. It never clouded the water. The fish & frogs never showed any affect from it - they just enjoyed their nice, clear water. There was always some algae left in the crevices and the areas where the water movement is greatest.

* By the middle of July, the roots in the skippy were filtering perfectly, and the waterlilies had produced enough leaves to cover 75% of the pond, so I did not have to worry about pond-wide string algae. I stopped adding the peroxide at this point.

� We just emptied the skippy filter & cleaned up the pond for the winter, and there was actually LESS detritus in the bottom of the filter than usual. (And 5 frogs-I think they thought they could hibernate there). Everything grew beautifully. The fish were happy. I was happy - I barely had to use my "official string-algae removal tool" (a cobweb brush) at all.

It works best if you put the peroxide in during the sunniest and warmest part of the day. It doesn't work nearly as well in cool water. DO NOT wait until the algae is out of control before starting the peroxide. It actually KILLS some of the algae, which means there will be dead plant material that your fish/filter/live plants will have to deal with. If you've let it go too long, remove as much string algae as you can the old fashioned way (manually :)), before you put any peroxide in. And don't pour peroxide directly on your plants, or get it on your clothes (it is peroxide, after all).

Sorry this post is exceedingly long. Hope this info helps someone else like me who fought the string algae and lost at one time.


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Thank you Jill for info. What is the concentration of peroxide that you are buying? I've only seen 3% solutions in the stores.

    Bookmark   October 24, 2010 at 7:19PM
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hollyhockdoll(z5 IN)

That's what I use; 3%. Guess it doesn't take much, really. If you can find it at a higher concentration, that's just fewer bottles to deal with!

    Bookmark   October 26, 2010 at 5:59AM
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I have a small 250 gal. pre form pond & I too have had success with using peroxide to keep the algae growth down. I use half a quart bottle of that WalMart 3% &dump it near where the water comes out of the Skippy filter (& make sure there are no fish directly where I dump!). I don't want the peroxide to kill the mint I have growing in the Skippy. I read to use this somewhere on this forum & it sure seems to work! I empty the filter in winter & toss the mint but I always have more in the herb bed to use the next year! I put the peroxide after it comes out of the filter as I didn't want to harm the filter/mint system in the Skippy. Have had clear water now for the past two years & only the short green stuff that clings to the pond sides that the fish love to nibble at. Thank you Jill for verifying the use of peroxide!!

    Bookmark   October 28, 2010 at 2:59PM
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