Treating an earth pond isn't that different from treating your water garden. Initially you should take some time to figure out what is causing the problem. Is there not enough aeration, is the pond in full sun with no plant life, do you have a muck build up due to falling leaves? The following components will all work together to improve water quality and help control aquatic growth:
Aeration is essential to a clear pond. Aerators and fountains will help maintain higher oxygen levels in the pond, aerators help particularly near the bottom allowing organic materials to decompose instead of accumulate. Aerating the water will allow beneficial bacteria to work faster at digesting the nutrients in the pond. Moving water will not allow mosquitos to breed like stagnant water
Bacteria - Adding beneficial bacteria to your pond is extremely helpful in removing excess nutrients built up in the muck. The muck at the bottom of the pond contributes to weed and algae growth. Beneficial bacteria will digest the muck.
Chemical Control - One of the most common forms of treatment for a natural pond is the use of safe aquatic chemicals. Most of these products are safe for humans, fish and pets when used in accordance with the label. Be sure to read and follow all instructions on the manufacturers label. Of course chemicals alone will not solve the problem. In fact, using either aeration, bacteria or chemicals alone will not usually solve the problem. These products used together are very effective at reducing problems, reducing future maintenance and improving water quality.