Kathy,I usually see this type of floating crud on the surface of my ponds in springtime, as the pond warms up.

These dirty looking clumps of algae floating to the surface, is usually caused by the air/oxygen present in the algae, that lines the bottom and sides of the pond, expanding with the heat of the day.
At night when it cools off and the algae sinks back to the bottom.

I have never tried using any chemical treatments to get rid of it.

I find that netting it out during the day time, with a fine weave net, can reduce the amount. Or if you have [or you install] a skimmer in your pond, it should pick most of it up during the daylight hours.
Vacuuming the sludge from the bottom of the pond will also help the situation.
If you pick it up with your fingers, you will notice that it breaks up into nothing, so fine filtering material is what is needed to trap it.

Pumping or skimming the water from the surface, through quilt batting and back into the pond will eliminate it.
Any of these methods have to be done over a few days until all the crud is picked up. The batting will have to be replaced or washed out frequently as it plugs up fast.

I don't think you can stop it happening again in the future.
Algae will grow on the bottom and sides of the pond continually, unless you are willing to constantly vacuum it off.
This build up of algae, will eventually let loose and float to the surface, as the weather and temperature conditions dictate.
Has your weather been cool then hot, back and forth like that? The fluctuations in the water temperature, seem to bring it on, as far as I can determine. That is why we normally see it in the spring around here, with one day warm and the next back to cool.
"Horton"

I was having the same problem. The pond water is clear and in the morning it looked great. But with a sunny day, when I came home from work, it was covered with the floating green flock like algae.

My skimmer baskets would be clogged with the stuff as were my brushes.

I read on the forum that there may not be enough O2.....the more O2, the more bacteria will get doing whatever they do. I had a large airator system that I was messing with a few years ago, I dug that out of the garden shed and dropped the air stones into the water.

They create a ball of bubbles about 4' in diameter, a whole big bunch of air. Well, it is either a coincidence or that was the correct diagnosis, the next after noon, only a tiny bit of the floating stuff, and the next day (today) nothing.

So, maybe I am on to something. If not, I am still happy.

When I built my pond I made a mistake and have a large area dead level, I should have had it all gently sloping to the lower end where my retro fit bottom drain sits. That is easy to keep clean. I should have installed this too when I built the thing, but did not know about any of this. But the flat area collects a lot of stuff and that is what floats up during the day.

My pond is about 6,000 gallons and I think I have had it now for 5 years now.

Perhaps you should try to cut down on the amount of sunlight available to the algae by providing shade through the use of waterlilies, water lettuce and other floating plants. This has helped cut down algae growth for me in the past. But, be careful not to overdo it. One summer after returning from a two week vacation to Mexico, my water lettuce had reproduced to completely cover my pond. This caused all my water lilies to go dormant too early in the season.

I have a lot of lilies. But it is May in ND and it takes a few more weeks before they provide much cover. My floating plants will be dropped in soon, the water just warmed up enough for them.

Shade helps a lot for sure.

Jim, that was interesting post about the aeration.
I think you are onto a solution for controlling that problem of bottom pond scum breaking free and floating on top of the water.

It is an unsightly mess when it occurs.
As the day warms up, the O2 in the scums cells expand and it floats to the surface.
As the water cools again at night the scum sinks, so it has to be broken up to stop the algae cells from ballooning up the following day.

I think what happened in your case is that the turbulence of the aeration broke up the scum particles and they were then pumped through and trapped in your filtering material.

Strong aeration and the added oxygen it produces in the water will always help to keep particulate algae in check.

I've had that floating scum problem in the ponds, a couple of times over the years and have used the netting out and filtering out methods, I mentioned in my previous post and it can be a lot of work.
But that aggressive aeration method of yours, sounds like it would be an easier way of dealing with the problem.

Though the problem is not an annual event, I now vacuum the scum/algae bottom of my pond in the spring ( but not the sides) to keep the crud from building up too much.I believe that also helps.
"Horton"

Horton,

You may be right with the turbulence. The air does move the water a lot, looks like a rapidly pot of boiling water. I am not going to over think, the floating stuff is gone!

I have a pond vac unit, I will probably get it out of the shed and clean up the bottom. It takes a lot of time. I don't mind the work but I don't have much time.

I bought a 2" diaphram pump that I am going to try to build a supper pond vac with. I have a lot of bottom and the shop vac type unit I have now is way too slow.

My wife always says I should hire a "pond boy" to take care of it. I would if I could find one.

But today it is sunny and hot - third day without the floating stuff. Lilies are starting to spread out nicely so there will be a lot of shade soon. Fish look very healthy too.

Jim

Jim, have you seen this DIY pond vac (linked below).
I got myself a secondhand, 3/4 HP, pool filter pump and experimented with a mocked up version of the vacuum this spring. It is powerful and does quite the job of sucking up everything from the bottom of the pond.

I had to filter the returning water from the pump through quilt batting to remove the debris etc that it sucked out of the pond.
If only there was a way of filtering the water before it enters the pump, as the priming pot basket strainer that is attached to the pump, is small and plugs up easily, with any string/coarse algae that gets sucked up.
Using the pump without the strainer basket to vacuum the gunk of the bottom works great, as that floating pond scum/algae stuff breaks up so easily, but as I said already the water has to be finely filtered before going back into the pond.
You must also be careful not to suck up any large pebbles, etc, that may damage the pump impeller, when you do not have the strainer basket in place.

Anyway take a peek, it may interest you if you have not seen it before.
"Horton"

Here is a link that might be useful: DIY Pond vacuum

Jim,
Your solution will do some good things for the pond. Algae as with all living plants when the sun is shining on it takes CO2 and converts it to O2. What you are seeing with the Algae is as the plant takes CO2 out of the water it produces O2. The O2 right next to the plant reaches saturation and no more O2 can be absorbed by the water and the O2 then forms a small bubble on the plant. When enough O2 bubbles form on the plant the plant becomes lighter then the water and floats to the surface. When the sun goes down the plant stops producing O2 some of the bubbles break off the plant and the plant absorbs some to produce CO2 and the plant gets heavier and sinks to the bottom again. The additional current produced by the air stone helps to keep the O2 level right around the plant from getting to the saturation point or breaks the bubble free from the plant and the Algae doesn't get light enough to float. The additional current from the air stone helps to get enough O2 to the bacteria in the pond for it to grow the way it is suppose to. This bacteria help to get some of the food out of the water that the Algae is living on.
Mike