Hey, Joe. This doesn't seem to have come up before. At least it isn't in the forum search record. So I did a search for an MSDS on Google. While used in swimming pools as an algae killer nothing is said about it's use in ponds so I looked a little further. One Safety sheet said there was some aquatic toxicity but except for the LDS50 rating of 70 it said little else.

There were a few details in several MSDS that were pertinent and that you should keep in mind. First it requires hot water to properly dissolve it. Second, it breaks down into hydrogen peroxide and soda ash with some referring to another chemical that is not consistent from manufacturer to manufacturer. That might be a problem. Third, soda ash is highly alkaline and will raise the PH of the water. While many pond fish thrive in PH 8, not all do. Fish react fast to changes in PH. You would need to be fairly cautious about the amount you add and how.

You really need a chemist to say yea or nay on a particular manufacturer's product. Personally I would hesitate. After all, Hydrogen peroxide is not that expensive and is easily available. You might do a forum search for Hydrogen Peroxide and string algae. A toilet bowl brush does wonders. As far as chemicals go, the less you use, the better.

Here is a link that might be useful: Hera Project Executive Summary

I hope you post your results. I don't personally think using an oxidizer is a great idea for the kinds of ponds I've kept, but like to read what others try. And I might keep a different kind of pond in the future.

Other oxidizers you may want to consider are Baquacil oxidizer and potassium permanganate. Not saying these are better or worst.

In addition to the excellent points sleepless made I'd add that if it does kill the algae it still needs to be removed from the pond. A pond full of string isn't a big risk to fish, but a pond full of dead and decaying string algae can be as it consumes O2. And later, after the string algae decomposes your water may not be very clear from all the tiny bits of dead algae.

The dose quoted may not result in a noticeable death of string algae. Normally oxidizer treatments are repeated until the desired result is obtained. A single massive dose can kill fish. And "massive dose" is related to how much stuff there is in the pond to react with. If the oxidizer reacts with stuff quickly there's less risk to fish. The longer elevated levels are kept the greater the risk.

You are on the right track if you do want to use an oxidizer. Many people seem to think a cup of 3% hydrogen peroxide will kill a pond full of string algae. The reality is large amounts must be used, right up to the edge of killing fish.

i found the info on a another site.sodium percarbonate uses in ponds.the post was written by chemist roddy conrad.there are photos and good info.i have never used any chemicals in my pond.

Joe, Thank you for that info. By following the name Roddy Conrad I found some very interesting and informative links, especially with my reluctance to use chemicals casually. Even the relatively harmless H2O2 can be improperly used. Baquacil is 27% H2O2. Do your math or mechanically clean and then spot kill string algae. Best non-chemical means for other algae is still UV followed by mechanical filtration, apparently. Certainly it seems safer.

I get a warning about SPAM when I type the name of another forum, so I will have to leave the searching up to you unless you e-mail me

I learned a lot from Roddy back in the day, good to see he's still around fighting the good fight. He used to get flamed a lot on every subject although he always provided his thinking, experiments and data. Flamers just bullied and character smears.

if you google sodium percarbonate uses in ponds,you will get the other forum with the post.

If you have fish in your pond use any and all chemicals with care. As for the UV Light it will NOT work on string algae as the algae is stuck to rocks, plant and the pond and therefore never goes through the UV. Properly clean your filter and do not over feed your fish these are the first two steps in the control of all algaes. Algae that makes the pond look like pea soup will most often clear out in about 14 days, string algae will clear out at the end of the world, keep at it and you will get it under control.

This site: http://www.ads.uga.edu/extension/newsletters/livestocknewsletters/2004NovDec.pdf, University of Georgia, says sodium percarbonate is alright for fish ponds at concentrations near algicidal levels, whatever that means.

Their idea of a fish pond is apparently someplace one raises catfish for food.

Where does one buy the stuff?

if you google sodium percarbonate,you will get sites that will ship 2lb cans.the site i saw the post on,is the wwkc web site.the moderator wont let me print the name.it is a good post

Hay Folks; If you want your fish shiny and clean, just dunk them in this miricle cleaner; and quicker than I can say it, your favorite fish will be better than new. And if you order now.....
OXICLEAN!

I had string algae in my pond. I got rid of it but it was time consuming. I took a toilet brush and one of those strainers with the handle (I use one just like it to strain tea leafs if my bags bust when making tea) I scrubbed the algae off the sides and while I was scrubbing I caught as much of the algae as I could in the strainer. I did this to the sides and to the rocks. It probably sounds crazy doing it this way but I tried everything else besides chemicals. About three days later my filter was stopped up again so I cleaned it and its been crystal clear now for about a month. My pond is only about 400 gal so it might not be so easy with bigger ponds. I don't like to use any chemicals so I try to just stick to good scrubbings, my filtration system and plants to keep it clear.