Natural String Algae Control?

Whiteside County, IL(Zone 5a)

My first season pond has done pretty well except for constant struggles with string algae in the second half of the summer

Our PH seems on the medium-high side. Everything else tests well.
I've been using barley bales with not so much luck.
Through the summer we've also used some natural biology (liquid), clumping clarifier and some charcoal for other reasons.
We're feeding the 6 fish once a day, but not very much. We also have some trapdoor snails.
It's about a 450 G pond with a 450 gph pump in pre-filter.

Our dogs that drink out of this and birds drink and bathe, so i really want to do something safe for them. We're not comfortable using some of the algae killers because of the pets.

Any ideas?

Here's a picture in mid-June when it looked good.

Thumbnail by Mrs_Ed
springfield area, MO(Zone 5b)

I have no tips on the algea from experience. Maybe water changes and more plants in the pond. ?

so how do you keep the rock from shifting around all over or ending up in the yard?

How deep is it?

Dearborn, MI(Zone 5b)

Hydrogen peroxide (the kind from the drugstore). 1/2 cup per 250 gallons. Remove as much algae as you can prior to treating. Repeat every few days.

Whiteside County, IL(Zone 5a)

Kneff, repeat every few days for how long? Ever?

Lily, It is shallow. 22" at the center, a 10" shelf and then a 4" shelf around most of the edge. We'll add a stream and water fall at a later date. I think the small rock just stays in place because of the grass. Every once in a while I have to move a few pieces around to cover the liner. Usually that's when someone or the dogs have been standing at the rock. Most of the bigger rocks around the edge were "dug in" a few inches so they aren't going anywhere unless it's into the pond. Probably too heavy anyway.

springfield area, MO(Zone 5b)

So at 22 " do you have fish in it? and if so how do you think the will do in the winter?
Just curious cause I would like to do another pond, but I don't want to make it as deep as the one I did last year. It is 3 and 1/2 feet deep.
But I just have goldfish in it. It is about 450 gallons also I figure.

Whiteside County, IL(Zone 5a)

We keep 4 comet goldfish in there and have two shubunkins. Our last pond was about the same size and we had goldfish and some koi. They did fine in the winters, but we do add a floating tank de-icer to keep the pond open. I have always read that it needs to be 1 1/2 feet for fish in the winter. Would have been nice to have it deeper just to be safe, but we dug it ourselves and we just pooped out! It is about 10 x 6

Dearborn, MI(Zone 5b)

Repeat every 5 or so days until the algae is gone. Be sure to hand-remove as much as you can first. More plants will also help.

Kemptville, ON(Zone 5a)

Mrs. Ed, you said you kept your fish in it over the winter? It's my first year with a pond, and I'm planning on bringing my fish in for the winter. My pond is about 28" deep, so I could keep them in it all winter. What do they do? I guess I'll need a de-icer. Your comments please.

Whiteside County, IL(Zone 5a)

Well. they just kinda hang out and go into semi-hibernation I guess. I'm not an expert, but we kept them for a few years (before we moved) with no problems. First make sure they are the hardy kind. Then, stop feeding them when it gets below 50 degrees. Add a deicer to keep the pond open, they need the oxygen. I suppose you can keep a bubbler pump going for a while until it gets really cold.

Funny story about the deicers. When we first were looking for one, we went to a nice greenhouse that had pond supplies and nice fish. Their deicer was 50 dollars. We took a trip to Farm and Fleet and found the same exact thing for 25! Now there are tons of different types out on the market.

Niles, MI(Zone 5a)

Kenny, here in southern Michigan we leave the water fall running 365, keeps the water open at the falls and the fish are now 10 years old and going strong.
As for the string algae, I treat twice in the spring with Algae fix (wont harm animals) and the rest of the season with barley straw, A mesh bag for washing nylon stockings, filled with straw and 1/2 submerged into the pond(1200 gal).
Keeps the algae down, plus having a good amount of surface plants really makes a difference. Keeping lettuce and hycainth over just doesn't work, I have tried for years. Best to just trade in the spring

springfield area, MO(Zone 5b)

do you have a UV filter in it? I don't think they get rid of string algae, but I just wondered if you had one or not. How do you keep the water so clear? Mine looks like pea soup. Can't see anything more than 4 or 6 inches below the surface.

Whiteside County, IL(Zone 5a)

Just ordered some GreenClean (Sodium Percarbonate) after much reading. We'll see how that goes.

Allentown, NJ(Zone 6b)

I use Koi Clay. I have a 3500 gal pond and the start of the season put in 1/4 cup twice a week. Follow during the season with one quarter cup a week. I dump it into the waterfall.

I've done this will all the ponds we've had for about 6 years.

Still have some algae but nothing drastic.


Whiteside County, IL(Zone 5a)

Thank Marian. I'll look into it.

Deer Park, IL(Zone 5b)

I have the plants, the UV filter, the good koi clay and still have algae but my water is crystal clear. The string algae is the worse.

BTW: Keep your bubbler on all winter in zone 5a, treat fish prior to winter with parasite medicine and pro-form "c" to make sure they are healthy going into the winter. Use Farm and Fleet de-icer and have a secondary one as back up. Preferable one with thermostat so that you aren't paying for it to be heating when not necessary. They do break and NEVER attempt to crack or hammer a hole in the ice-it will stress and potentially kill the fish. Use hot water from a kettle or from the stove to melt a hole back in ice or simply add the new de-icer and it will quickly re-melt a hole in the ice. Cold temperatures with periodic warm temperatures are the worse conditions for the fish. The warm spells quickens the rate in which disease/parasites can attack their hybernating bodies. This is the primary cause of fish death in winter/spring.

PERTH, Australia

Nice pond, Mrs Ed. Pity that lantern on the right is crooked!

Whiteside County, IL(Zone 5a)


Thanks, Monk.



Before you use to much of that algae control ... consider this. String algae is a sign that your pond is well balanced (which means your doing a great job with your pond). String algae has loads of beneficial bacteria and thrives under circumstances that provide large amounts of nutrients. For example ... a decaying log is an excellent source of beneficial bacteria. The rate of decomposition is slow enough that the log is constantly releasing nutrients into the water for a long period of time and feeding everything for a long period of time. Remove the log and you have decreased a certain percentage of the algae's life support.

I did not see any logs or leaves in your water and the plant material was minimal, BUT ... I did see something that could possibly be supplying nutrients to your water garden.

I noticed that your pond seems to be right at ground level - in other words the water level and the turf surrounding your pond are are almost at the same elevation. Ideally ponds should be installed so that the surrounding water cannot leach into the pond. You could be getting a fair amount of nutrients when it rains or when the turf is watered or if the pond is in a swale that leads surface water right to the pond. Basically water from the surrounding turf could be running into your pond.

Another thing is definitely the birds and other animals getting in the pond (I am impressed that it is still as clean as it is).

Some things you could try is adding shade (although I have seen string algae will grow in part shade situations) or even changing out the pots that your plant material are growing in (sometimes string algae is brought into the pond environment by purchased plant material. Another thing to try is cutting back on the feeding and let the fish (especially if they are koi) eat the algae. We have 15-20 fish in our pond at work (it is 6' x 10' x an average of 1.5' deep) and we only feed them once every week or every other week. My favorite algae controllers are natural bacteria that feed on ... algae. Most likely you will still need to use a commercial algaecide, but its all part of the hobby.

Whiteside County, IL(Zone 5a)

Thanks for the info Shrubbs. I do think that the pond gets runoff. It used to get cloudy after rain, but then we turned up the pump and it did better.

The string algae started out slow so I did not have much problem with it. But then it got pretty thick and was on the shallow small rocks and it just looked kinda swampy. I couldn't even see the fish.

Sounds like I was feeding the fish too much. I only have comets and shubunkins. Have a few trapdoor snails and some baby ones. Maybe that will be enough to eat up some of the stuff.

Niles, MI(Zone 5a)

Me Ed. Do you keep your filter running all of the time? my pond is 10 years and running all of the time ( 9 x 12 x 3) with waterfall and a water spurter. Once in the spring I treat with algaefix and the rest of the year there is a bag of barley straw in the water,under the return from the waterfall, so the water runs through the straw. I change the straw every two months and have very little problem with the string algae. I have koi, shubukins and comets and all of the frogs you could want. We don't feed the fish much, maybe every three weeks, between the mosquito larva the tadpoles, and the good algae there is plenty for them to eat. I agree that run off can effect the water, fertilizer from the lawn can "add" to your pond and give the algae something to feed on.

Whiteside County, IL(Zone 5a)


well as you can see, I don't yet have a water fall and skimmer in this pond. Instead I have a pump housed int a filter box. yes, it runs 24/7. It will get turned off pretty soon though as the water temp hits 39

I tried the barley, it didn't work too well since I already had algae there, I guess.

I forgot to say that this pond gets sun from about 2-5. Imagine how it would look with full day sun. yikes. I told my husband that he needs to build me a big ol' pergola with shade cloth to cover the pond. He was not amused.

: )

I like the pergola idea ... I was actually laughing because that is the typical response I get when talking with clients - she would like a pergola and he is not too happy to hear about it.

Whiteside County, IL(Zone 5a)

hahaha! yah, that's us. you know why I finally got this pond (even though it doesn't have the waterfall)? Because HE got a 52" TV.

Grand-Falls, NB(Zone 4a)

Iol Mrs-Ed, typical male. I have one like him too.
I'm also dealing with string algae. It collects on the rocks in the waterfall, and in the pond below the fall. I did have a piece of drift wood in the water for the birds or other animals that might fall in. Never thought it might contribute to feed string algae.
I have a UV light inside my filter, at the top of the fall. I only run it during the day. It didn't help with the string algae, but it did help clear the water.
I have read somewhere, on these threads, that some use Peroxide. Is that safe for the fishes?

Whiteside County, IL(Zone 5a)

I think that peroxide thing is a part of this whole Sodium Percarbonate thing.

BTW, I tried that and nothing happened. I'm not sure if it was too late in the season because we only had about 45 minutes of sun on that location by that time of the year, or the water temp was so cool, or it was just a bad product. I guess I'll just start over next year and see what I can do.

I just uncovered the pond from the fall covering. I had a shade cloth over it, with a spot open for the birds. I was glad to see that I didn't have too many leaves blow in.

Deer Park, IL(Zone 5b)

Mrs. Ed--

I have a non-used toilete brush attached to a long pole and I use it to clean/dislodge the algae. It's a lot of work in my deep pond but essential once a week at the least. Your pond isn't too deep and it might be easy to wade in there and brush it up and use a skimmer net to get it out. While it doesn't solve the problem it might help a little. I have it all-the skimmer, the bottom drain, tons and tons of plants, UV lighting and barely and koi clay (in all the best known brands). While it didn't solve the problem this past summer it did help a lot. I feel that if I would have started earlier in the summer in treatment and being more pro-active my problem would not have gotten so out of hand. Next summer I will be more aggressive and structured in treatments.

Holland, OH(Zone 5b)

For green soup algae a UV is best. I eliminated string algae several years ago with Aquascapes SAB Extreme.
The link is just for information. Like everything else shop around the net for the best price. I absolutely guarantee you will have no string algae and very minimal bottom sludge with this stuff. Pricey, but well worth it. I use about 5Lbs. a season on a 2500 gal full sun pond that otherwise produces string algae by the bushel. Does not harm any plants or any aquatic life. Totally organic product. Just dose every two to three weeks depending on your fish load and amount of sunlight. String algae never appears. There's no dead algae to scoop or scrape.

edited to add:
They are having a heck of sale. I've ordered from them before. Decent place to do business. I just orderd 2 yrs worth. Couldn't resist the bargain.

This message was edited Dec 26, 2009 7:01 PM

Holland, OH(Zone 5b)

Wasnt' sure the link was working.

This message was edited Dec 26, 2009 7:02 PM

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