Yes there are long term problems with this! Karmex (Active ingredient: Diuron) is an extremely bad chemical to use in your pond. Not only is very illegal to use in and around your pond, it is hazardous to your health as well! Karmex has been shown to cause cancer, and is very capable of entering the groundwater that runs underneath the pond causing problems with the neighbors as well.

The biological effect is substantial. Karmex will kill almost every plant touching the pond. While this seems like a great idea, the problem lies in the few things that survive. These survivors are extremely hardy, and honestly if Karmex wouldn’t kill them, nothing will. Eventually these plants will take over the pond, and there is not much you can do to stop it.

Karmex is a soil sterilant that was disigned to kill farm fields where no chance of runoff will occur. Sadly, many small stores and elevators sell it as a pond product, not knowing how extremely bad this chemical is for humans and the environment.

Avocet and Kraken are approved aquatic chemicals that will kill the plants around your pond in a safe and less environmentally harsh way. Stick with them and you’ll find yourself much better off in the long run.

For duckweed I would refer to this post (Controlling Duckweed & Watermeal). It talks about how to use WhiteCap to control duckweed.

Hope this helps!

To kill water lilies the best product to use, if you don’t have to irrigate, is called Kraken. We highly suggest to mix Kraken with a surfactant called Cide-Kick for best results. Cide-Kick will allow the aquatic herbicide to be absorbed by the water lilies better for optimum control. To treat approximate 2,500 sq. ft. we recommend mixing 4 oz Kraken, 2 oz Cide-Kick Surfactant & 1.5 Gal water into a tank sprayer. Spray to completely wet the leaf surface of the water lily. The above is a recommendation, I would always suggest to read the kraken label. If using your pond water for irrigation, another option would be to use Avocet. The dosage rate is a little different, but the same concept. You would use 8 oz Avocet, 4 oz Cide-Kick & 2 gal water.

Hopefully this helps you Wade!
Thanks for your question.