Water Clear But Algae Still Forms

skiwindhamApril 16, 2010

We have a strong filtration system including UV lights.

Our water is crystal clear but...

Algae keeps forming.

It sticks to the liner, plants, etc.

I'll vacumm it out, but the next day it fills right in again.

Not tested the water (wouldn't know what to look for).

Any thoughts on killing/removing algae that forms in crystal clear water.


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You don't specify what kind of algae is forming.

If you have clear water, then you have eliminated the free floating algae which is what most people don't want.

The low blanket kind of algae that covers the liner, rocks, etc is natural and that is healthy to have in a pond, especially if you have fish as it is a source of food.

String algae is desirable to some people and that is long filaments of algae. You can leave that or not. A lot of people remove that with a toilet brush. If I have string algae and want to get rid of it (usually I leave it alone unless it gets out of hand) I get a branch with lots of twigs, twirl it around and the algae sticks to the branch which I throw away.

If you don't have fish or other living critters in the pond and no animals will drink your pond water, then you can use an algae killer. There are many kinds available, however it is poisonous to mammals, insects, birds, fish etc.

I hope someone with more information joins in to fill in the gaps on my knowledge.

    Bookmark   April 17, 2010 at 9:39AM
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I agree with Pashta. That kind of algae is good and normal. If you have that and crystal clear water it probably means you have a nice healthy pond. I would be happy with the clear water and leave that algae alone.

    Bookmark   April 17, 2010 at 11:29AM
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jodi_4(z4 Mn)

some algae is fine (not string algae), but if the fish are not able to keep it to a minimum by eating it, it will just take over. The best natural way to control algae, both string and the kind that coats the walls of the pond and anything else not moving, is to use koi clay. I have used it for years, and it is wonderful. Not to mention you can't overdose or harm fish or plants with it. It is what koi ponds in Japan have been made with for centuries. It is actually GOOD for your fish and plants.
Make sure you get Calcium Bentonite Clay (100%), Natural Mineral, Montmorillonite. I have found a few sources online and some local fish stores carry it. I wouldn't be a ponder without it.

and no, I don't sell or benefit from it's sale in anyway.

    Bookmark   April 19, 2010 at 3:59PM
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Bentonite clay? How much do you use? I suppose you could get some from cat litter, if it isn't contaminated with chemicals? How do you use it?

    Bookmark   April 19, 2010 at 4:15PM
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jodi_4(z4 Mn)

I would be careful using kitty litter as there are other things in it that could contaminate the water.
It depends on how bad the algae problem is to start with. But normally for the first bloom in spring when the ponds here are starting to cycle, or for a new pond just starting it's first cycle, and algae is blooming long before plants have gotten going and covering at least 50% of the water surface you would use 10 tablespoons per 1000 gal. daily till the algae is gone (usually a week or two). If your bloom is really bad and it is not completely gone by then, just continue with the same dose till the algae is gone. Then once the algae is gone use 2tlbs. per 1000 gal. once a week. It does not get rid of green water, you need a UV filter for that, and you must vacuum the bottom of all that dead algae otherwise it will just be food for a whole new crop. Once I started using it I have never had a serious algae bloom again. Before I used it, I would see the algae start even before all the ice was off the pond. I use it in the evening, cause it will cloud the water, but by morning it is crystal clear and sparkling!
Not to mention in intensifies the color of fish and the trace minerals feed the plants making them bloom abundantly every year.

    Bookmark   April 19, 2010 at 7:42PM
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Hi Jodi,

Thanks for the info! I have the green carpet algae too. It never surprises me to see how quickly it will grow and completely cover everything here in the frigid north!

I don't mind the algae horribly. I think it gives the pond a "lived-in" look. But, I really HATE it when I have to get in the pond for any sort of maintenance work. It is slippery and dangerous when it gets on the liner. Since I have had a history of serious back issues that have required surgery, slipping and falling in the pond scares me to death!

So...just a couple questions if you don't mind. How do you know when its okay to vacuum the dead algae? What does it look like? How often do you need to vacuum? Do you have a specialized pond vacuum? I only ask because I don't think that is in the pond budget for this year. So what I really should ask is can a good old shop vac do the trick for sucking up the dead algae? Would you care to share some of your online sources? I live in the middle of nowhere in northwest Wisconsin. The nearest Target is over an hour and a half away nevermind a pond store!!


    Bookmark   April 22, 2010 at 4:07PM
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jodi_4(z4 Mn)

I don't mind at all, and I know what you mean. A little goes a long way!

As for vacuuming, I do it two or three times a year on average, unless some big wind (and we get a lot of them here) blows in lots of leaves and debris.
I have a matala muckbuster, it was a BIG investment and took some scrimping to get it. Have you thought about making a "floyd's pond vacuum" using a regular shop vac? It looks like that could work. If not and your pond isn't too big, and you don't mind emptying it A LOT, then sure use a shop vac. I know other members have used a variety of different types of pond and pool vacuum systems. I had tried a few of the "cheaper" types, and they were either very difficult to work or just didn't really work at all, that I finally bit the bullet and got the heavy duty pond vac. I did get it on ebay for a pretty good price.

I always vacuum at the start of the season just after the water thaws out, cause the water is 100% saturated with oxygen. That way if I stir up some of the muck, which is going to happen, it doesn't harm the fish. Then definitely before it starts to freeze again in fall, and then when necessary in between. I don't think you have to have a perfectly clean bottom, just don't let it build up to where you have mud on the bottom.

As for knowing when the algae is dead, it will turn a yellowish brown and not stick to the sides or rocks. If you vacuum and it is sticking, it isn't all dead yet, so keep "overdosing" with the koi clay.

Here is a link that might be useful: floyd's pond vacuum

    Bookmark   April 23, 2010 at 4:37PM
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horton(6 b Ontario.)

Flloyd's vacuum looks like a great idea, but I would not place any electrically powered machine that close to a pond, as shown in his photographs. It would be too easy for it to topple into the pond and cause all sorts of problems.
Securing the vacuum by tying it back from the pond, so it cannot fall into the water, would be a good idea.
Be sure any electrically powered pump, UV light or vacuum, etc, is plugged into a GFCI receptacle or GFCI breaker controlled circuit for your safety around water and electricity.

    Bookmark   April 24, 2010 at 8:01AM
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This is a perfect post for me. I have crystal clear water but alot of algae growth. I drained my pond this spring and got out most of the muck. How sad to see the algae back already. Is the stuff that floats on the top the dead algae. I can skim tons of it off but it always comes back. I will try the koi clay. How do I know how much water is in my pond?


    Bookmark   April 29, 2010 at 6:05PM
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jodi_4(z4 Mn)

Try this site:

Here is a link that might be useful: pond calculator

    Bookmark   May 1, 2010 at 12:00PM
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Have you ever tried barley straw pellets?

Sting algae was prevalent last year, particularly in the stream. It was already doing so this spring. I removed most of it mechanically (toilet brush), then added the barley straw. I only used about half the recommended amount. It's supposed to take about 30 days to take full effect. But the algae never came back.


    Bookmark   May 11, 2010 at 10:24PM
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