Aquatic herbicides and algaecides are useful tools for pond management. A chemical application may be your best option to gain control for the short term of a pond that has become overrun with weeds or algae. The dead decaying weeds and algae that have settled on the bottom of the pond are creating muck in your pond. That in turn increases the chances for future weed and algae growth. Every time weeds and algae are treated, they fall to the bottom and if they are not removed mechanically, they will bio-degrade and encourage future growth. Chemicals are an important part of most management plans but they can't be the entire plan.
When treating weeds and algae, sudden changes to water conditions can negatively affect other aquatic life in your pond. It's best to run your aeration system during all chemical applications. It will help maintain high oxygen levels for fish and other aquatic life as well as help in the effectiveness of the application.