We own a 3 acre pond that is 20 feet deep at the deepest point. It has a serious algae problem with heavy blooms all summer, including blue-green algae later in the summer.

We had a biologist with a local university do some sampling. She told us the algae was the most she's ever seen and the phosphorous level was also the highest she's ever seen. There was almost no dissolved oxygen below three feet.

Question: Will a chemical treatment take care of it, or do we need to install an aerator? Or both? I'm a bit concerned about the cost of an aerator.

Chemicals are considerably cheaper, of course, but if I need to treat the pond several times a year every years, the cost of chemicals will certainly add up, too.

Appreciate any help.

Do you know the source of the P or can you call the biologist and see if she knows?

Even if you get the algae under control, if more P is coming into the pond the problem will continue to occur.

I would look into methods to remove or bind up P in the water to make it unuseable to plants, which might also include mechanically removing plants/algae as it grows and getting it far enough away from the pond so that none of it will run back into the pond via rainwater after it decomposes.

The cost of chemicals WILL add up, as the treatments will be every few weeks, not a few times per growing year.

Tilapia (if legal to stock in ponds in your state) are a very good choice to remove P from ponds as they die every Fall and are typically removed from the ponds by scavengers or by anglere before they die and put on the dinner table. Typical stocking rates around Northern Indiana are 40# per surface acre or more if the algae is bad.

I do not know the source of phosphorous. There is a small feeder stream, but it originates in woods and is mostly groundwater runoff. No ag or livestock or any other point-source possibility. We don't fertilize around the pond, either.

The biologist said the high P level could be a result of the algae cycle itself. Something about once the algae gets started, it continues to feed off itself and increase the P levels.

The pond is around 40 years old and has trees around 3/4 of the bank. The leaf litter may be contributing to the excess nutrients, perhaps?

Thanks for the quick reply.

BTW, there are no other aquatic plants in the pond and removing planktonic algae would be difficult at best, wouldn't it?

It is not filamentous algae. It's all suspended.

Welcome to the forum!

Yes, the trees will contribute a lot to the high P levels. Leaves in the water decomposing.

Raking algae out, removing some trees to minimize leaves in the pond, adding Tilapia every year, etc., etc.

Alum treatment can help bind and sink Phosphorous and improve problematic planktonic algae blooms by rendering it unavailable. Seek a pond management professional in your region - David Beasley is a good choice and I believe his company is listed in the resource guide [www.solitudelakemanagement.com]. David is a great guy and good friend of mine - you'll be in very capable hands.

IIRC there was a recreational lake in Fremont NE that was closed for several weeks over a few seasons due to toxic blue green algae blooms. It was treated with Alum and believe it was successful. Alum treatments can lower your PH levels and cause fish kills, so adding lime to buffer the swing is sometimes necessary. Again, best left to a pond management professional. Here's the article on the NE alum treatment - hope it helps:

http://water.epa.gov/lawsregs/lawsguidance/cwa/tmdl/nebraska.cfm

Tree leaves and nutrient recycling are the likely sources of increased phosphorus stimulating algae growth.
Phosphorus testing can be deceiving. Phosphorus measured as total P includes all the phosphorus in all the organic material of the sample including the algae. So when algae is abundant total P is usually abundant due to all the P in the algae. IMO the proper P measurement is ortho P (aka dissolved P or soluable P) which is the available phosphorus that is being used or available to the algae for more growth. Both types of phosphorus can reflect the trophic conditions, each providing different information.

Alum treatments do reduce the phosphorus in the water column and precipitated alum forms a layer on the sediment helping to seal the top layer on the sediment slowing the release of P from decay. Note this works best in deeper waters and is temporary. As phosphorus laden inputs persist P increases and the problem resurfaces or reoccurs. Often the best long term approach for an old hypereutrophic pond is rebuilding. Rebuilding should be done so phosphorus inputs are minimized. To reduce expense of pond rebuilding, the pond can be down sized. Large ponds cost more to maintain when anything has to be done. It is the rule. Bigger is not always better.

Whenever you get the algae under control aeration and algaecides are some of the tools in the pond management tool box. Aeration by itself can only do just so much for improving a pond. In big problem situations other tools are needed.

Hey everyone.
I am having the same problem. We are using vertex twin aerators and top water fountain but we still massive plankton algae looking where the fish are starting to get lighter. We have tried Cutrine plus with no change at all. No runoff into the pond, no livestock.

What dosage did you apply? Depending on the type of algae and quantity, you can apply between 0.2ppm and 1.0 ppm.

I used one gallon over half and then did two gallons on the other half. One acre pond. I did this twice with no changes. I think it increased.

What's the depth of the pond? (max and average)

Max is 18 foot. Average is 8-9.

We have high akalinity and high ph 8.6. We have a soda ash water well.

Application rate is from 0.6 to 3.0 gallons per acre foot of water. It's on the label of the container. You have approximately 8 to 9 acre feet of water in the pond.

Here's an electronic copy of the label. Read the directions, and pay attention to the part where it tells you how to apply it.
http://www.lonza.com/~/media/Files/water-treatment/Cutrine_Plus.ashx

I've found that it seems to work a bit better if I use 1-2 fl. oz. of surfactant per gallon of tank mix.

Depending on the amount of algae coverage, you'll need between 5 and 24 gallons of Cutrine plus per application.

Thank you