Henry, welcome! I sympathize. I broke my back. Ain't life wonderful?
Don't empty the pond. Swimming pool chemicals are a no-no. You don't say what kind of algae. What size is the pond? Is it lined or a preform? How deep is it? Do you have a pump and filter? What size and type? Do you have rocks on the bottom? Do you have a UV light? Did you have an earlier algae bloom or has it been this way from the beginning of the season? Please answer and some one will be along soon. Sandy

Thanks. I don't have a filter. The algae is long stringy strands as well as green water. My pond anti-algae stuff doesn't phase it. The pond is about 75 sq ft and an average of 15 inches deep. It is lined, I have rocks and no UV light. This bloom really began last season as I lost control of the algae problem then.

String algae is a pain.. you will probably have to manually scrap it off.. the bloom I wouldnt worry about as it just cosmetic but string algae you have to manually rip out.. a UV will take care of the bloom but not the string.. I had a bad case a few years back and had to rip out filter media and tons of algae by hand..

Question-- If the pond was drained and hydrogen peroxide poured on everything wouldn't that kill the algae? Sure it still has to be cleared out but at least it would be dead. Right???

BSF, I figure if Henry is going to have to drain the pond he may as well just scrub the sides and remove the sludge from the bottom and star all over again. No need for the HP treatment in that case.
With no filtration and rocks in the pond [are they on the bottom Henry?] there must be all kinds of nasties lurking in the crooks and crannies, just waiting to start up trouble again with any freshly added water.
At only 15 inches in depth, algae will grow very quickly. Especially if the pond is in direct sun without any aeration?

Henry, in my opinion, I would say drain, scrub and start all over again, but this time add a pump filtration and more so, aeration in some form, because of the shallow depth of your pond.
No rocks on the bottom, if in fact they are there.
With the pond being only 15 inches deep, plus no movement/aeration of the water, rocks lining the bottom of the pond, are a catalyst for all kinds of trouble [parasites and disease] and the promotion of algae growth.
"Horton"

In my opinion hydrogen peroxide would probably work, but not at the concentration you buy at the drug store. 0.03% isn't strong enough unless you put in a TON of it. Oxidation ocurrs the second it hits anything organic and it turns into water and disolved oxygen almost instatly. I have been told that as long as you don't have any plants in the pond, then adding hydrogen peroxide once a week and help maintain a pond because 1) it oxidizes orgaincs, and 2) it adds dissolved oxygen to the water....you can't do this after you add fish though or you will kill them :(

Thanks everyone. The pond averages 15 inches but it is over 2 feet at the deepest part and I do have aeration in the form of a mermaid fountain. I have scrubbed out a lot of the stringy algae and sludge and now it looks pretty good but the water is a bit brackish. I'm thinking that this might not be so bad because it will allow the fish to hide better. Soon I will begin to use the water on the roses and replace it with clear water so it should clear up some. So I think I'm going to let it be and tomorrow I'm getting some new fish and hyacinths.

I think I am getting a headache. Henry, brackish water is not good for the fish. It is still filled with pathogens. Does it have a hint of sulphur or swamp gas when you smell it? You don't say anything about adding a filtration system. The rotting particles will only sink into those rocks you don't say you removed and in combination with fish poop you will have a sewer that will clog the mermaid fountain eventually. It won't make the fish happy but you will get happy algae again because it is still right there in the goop in the rocks ready to bloom again with some light and poop. Do you have a water test kit? Without doing frequent testing your problems will continue, especially since you are ignoring what we are telling you, why it is happening and how to fix it. Horton gives good advice. You should follow it. Sandy

If you keep the pond without fish then I suggest lots of plants to help clear the water. Water Cress, Water lettuce, Water Hyacinth. Drop a few oxygenaters in who will love the sludge on the bottom. A few lilies. In the fall you will have to net out the WL and WC. But your pond should clear nicely.

Next ponding season you should be fully recovered and then decide on where you want to go with your pond.

Regards,
Lisa

Sandy, hope your headache has subsided???
Remember the old proverb about taking a horse to water.......LOL
"Horton"

Hi,
Do you have any thing filtering the water at all. Most pumps are capable of having at least a small box filter attached to them. When I started my pond I had a little fountain pump, I ran a short bit of tubing off the intake and got a chunk of foam to put over it. It may not sound like much but it kept the water clear until I got the rest of the system going. I had to clean the foam every couple days but it might help get the sludge out of the water. You can rinse the foam out in a bucket and water the roses with it as well. Look for a fairly open cell foam and you should not have to clean it as often, a 1 foot piece at 1 inch thick would probably really help, relatively inexpensive at a craft shop. Just remember to ask if the foam is treated with anything. Good luck.

Just a point of clarification regarding hydrogen peroxide, the typical concentration that you buy in the drugstore or supermarket is 3% not 0.03% unless you wish to express it on a decimal weight basis then it is 0.03 wgt/wgt. Typical concentrations that work well for removing string algae (but not effective on suspended algae) are about 1-2 pints of 3% per 1000 gallons although doses as high as 1 pint per 100 gallons has been used with no reported adverse effects to common goldfish (comets) and koi or typical plants in the pond. When you add hydrogen peroxide the reactions are fast but not instantaneous; the rate reactions result in the initial formation of water and atomic oxygen which has numerous side reactions one of which is with itself then resulting in the formation of the typical diatomic oxygen molecule or it can react with various catalytic agents to form a highly reactive compound known as a hydroxyl radical. Commercial/industrial hydrogen peroxide varies in concentration from 8% to 60% or more with the very high concentrations having a viscosity approaching a heavy syrup.

The exact mode of operation on algae is not clear but there are several concepts floating around about lysing of cellular attachment, etc. When it is added to a pond it does not mix instantly. In fact, best results are achieved by adding in the immediate area where the string algae exits. Therefore the concentrations that are present are much higher than what would be predicted by simply calculating the amount added divided by the total pond volume. In swimming pools using Bacquacil (a quaternary amine disinfectant) hydrogen peroxide is sometimes used to remove chlorine (hypochlorous acid, chloramines) but at vastly higher doses - gallons of 10-12% added to a pool. Hydrogen peroxide can be used for disinfection but again at very high doses. However, for string algae control the dose used is not meant for disinfection but to disrupt the string algae which it does with very good effect. The down side is that the resulting "soup" will exhibit a high oxygen demand (BOD) and you will have another algae bloom resulting from the release of nutrients. For these reasons it is important to remove as much of the string algae as possible by hand before treatment and to have plants available or other means for taking up the released nutrients (or flushing them out).

Henry, if you intend to operate a pond without circulation, without filtration, etc..... all the things suggested by Horton and Sandy... then your pond will continue to present you with problems. It is possible to have a pond with no circulation or biofilter per se but as also mentioned you'll need lots of plants such as water hyacinths and/or water lettuce to take out nutrients (consider them as a floating biofilter if you will). I have seen such ponds but you can only support one or two comets - i.e., a very few - and not feed them any food. Plus you need to balance the shade/sunlight issue: enough to keep the WH going but not so much as to help the algae too much. Good luck.
---David

Here is a link that might be useful: A website for industrial hydrogen peroxide - an example

Geez... I am not ignoring anything you pompous jerks. I got rid of the stringy algae and the sludge or at least 90 percent of it. This included a lot of leaves and rotted wood chips which were from the mulch I use in the garden. I assume the brackish color is from tannen which I have hopefully removed the source of. The only rocks were around the edges which I was using to anchor plants. This year I am using only hyacynths so I got rid of the rocks. I don't have anything against filters but the idea of either wrapping the pump or using the fountain for a filter seemed good. However I will probably get a filter if it looks like I can't get along without one. As far as I know you can't filter out tannen anyway but I will replace most of the water the first time I use the pond water to water the roses. This should eventually solve the problem. Last year the pond did very well without a filter. You can have this forum.

Hmm. well that went well.

Prof, you are my "Hydroxyl Radical" [think good!]

Henry, don't go away mad, we were only trying to pass onto you, what we considered, was the best advice, in answer to your original message, seeking advice about the "huge algae problem" you were encountering and your follow up post, where you mention having rocks in your pond.

In your third post, it seemed as if you had decided, that it was all too much trouble and you were just going to [more or less] leave things as is, with just the removal of some of the problem algae, but not the build up of sludge on the bottom of your pond.
You then went on to say that you would probably just "let it be" and introduce new fish into your pond.
A pond that is, it would seem from your own description, an environment that could be considered to be toxic to fish.
The sludge would still be on the bottom of your pond and who knows what injurious pathogens it may contain.
That scenario, is not, in any ones opinion, a good or caring idea.

You can call me any names you wish, but I, and I believe, the other posters, were giving you their best advice and subsequently the most honest assessment of your reactions to that advice.
"Horton"

Henri, the bottom line is and always has been: if it works for you and you're happy with the results then that is all that matters despite what us pompous jerks might have to say or want to suggest. I did not mean to insult you nor do I believe that anyone else did.
---David
P.S. Many years ago I lost several hundred seedlings because I started watering them with water from my pond. I was too lazy to go back to the house and get water from the tap. I forgot to realize that the water (pH = 8.3, highly buffered) would overwhelm the soil conditions. This probably isn't the same as watering in the garden since the seedlings were in a potting mix which doesn't have the same buffering capacity that plants in the ground. Just passing that along for what it's worth.

Sorry we insulted you, I must admit it did sound like you had a do not care attitude that the pond was more important as a water source for your roses. I think the wording of "brackish" was taken differently than you meant, I think you meant colored water not salty or full of sludge. We all truly wanted to help you solve your issue, give this site a chance it is very good. Most of the people here run a fairly tech system but they are willing to help us low techs with any questions and offer help on anything.

HENRY - In due respect, I've learned everything I know about ponding from this forum - bottom line if you're not prepared for the answer, then don't ask the question

Hey - I learned a lot even if Henry took off without.

For instance, I had no idea it wasn't good to water my potted plants (in potting mix) with pond water - thought I was really nurturing them. From now on the pond water will go to trees and shrubs.

Thanks David, and the rest of you. Much good info. Min

I've had a pond for years that I made with a liner that is only 20" to 30" deep and 4x6 wide - always had goldfish and never had pump or filter until a year ago when i wanted it for looks. I lose a fish or two every summer but more always coming along. Mix of shade and sun. Only had algae for about 6 weeks the first year - put plants in and it settled down by itself. I've never understood the need for treatments of any sort. Nature knows what to do if you work with Her -in my opinion. Also, if you clean a pond you lose all the great stuff in the muck - larvae, eggs, etc.

Good tip about watering with pond water - thanks!