Green Film… Algae… My Pond is Turning Green…

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The weather is getting warmer and if you have a pond with a weed problem, it’s time to get proactive about it! My phone always starts ringing with questions about the green stuff on people’s ponds when the weather starts to break, and now is the time to get ahead of the problem. There are many different weeds that live in aquatic environments and while they serve a purpose of feeding fish and other pond visitors, they can also be unsightly and detract from the pond.

Magnifying Glass


Make sure that you know what weed you are dealing with! Different weeds require different treatments, and if you have treated your pond before, you know that it can get really expensive, really quick. Getting the right ID will allow you to treat it right the first time. You have a couple options to get an ID, snap a few pictures of the pond and your weed/s and you can email them directly to me (, usually I’m able to determine the weed from the pictures and offer you some options to get rid of it, if not. You can also get a sample of the weed in container with a tight fitting lid, and bring it by the office. I’m out and about a lot during this time of year, you may have to drop it off and leave me a number or email to get back to you on to discuss what options you have available.

Picture of person pouring a pond dye into a pond

Pond Dyes

I strongly encourage you to be proactive to try and suppress weeds in your pond by adding a pond dye to your pond now. A dye works by reducing the amount of sun light that is able to get the bottom of the pond, where weeds will overwinter. If sunlight is able to penetrate, then as the water temperature warms up, the weeds come up and you will start to notice them. There is one caveat to pond dyes, you have to maintain a certain concentration, in order for them to be and remain effective. Over the years, I’ve had people that put a pond dye in early on and it worked great, but then later in the spring when we had a lot of rainfall, the concentrations in the pond dropped and then the weeds took over. I wish that there was a catch-all but pond dyes aren’t it, you have keep an eye on it, in order for it to work.

Picture of Triploid Grass Carp (Fish)

Grass Carp

I get the question each year about adding grass carp to ponds to manage weeds, and they are effective, but only on certain weeds. Grass carp will eat weeds that grow under the water, and usually will add balance to a pond, but they very seldom will eat weeds and algae that are on top. One other thing that I get questions about with grass carp is how long they are effective. People will say I added carp in the pond 10-15 years ago, and they are huge, but they aren’t controlling weeds anymore. Grass carp are typically only effective at controlling weeds for about 8-10 years in a pond, after that their metabolism slows down and they will eat less and less. The recommendation is about 15 grass carp per acre of pond, so when you start getting close to the 5 year mark of putting carp in the pond, consider adding 5 more, then over time you can fish the older one’s out that aren’t doing their job anymore and keep that stocking rotation going so they continue to provide effective control.

I’m always happy to answer any questions that you have and offer suggestions on how to rid your pond of weeds. You can reach me via email at or by calling our office at 336-570-6740.