New ponds can get cloudy or have algae blooms because the Biological filter is not working yet. Below is an explanation of the Biological process.
Biological Filtration refers to the process whereby organic matter containing nitrogen is broken down and converted into less and less toxic forms of nitrogen. This process contains several stages, and begins with the introduction of nitrogen into the pond in the following ways.
1) Urea and fecal matter produced by the fish.
2) Protein from decomposing (excess) fish food.
3) Protein from decomposing fish and/or plants.
Ammonia is a byproduct in the first conversion. Ammonia is very toxic to fish, and the higher the pH, the more toxic the ammonia. Ammonia is converted to nitrite by friendly bacteria called nitrosomonas. These bacteria live primarily in your filtering medium: bio balls, floss, foam filter pads, etc…They are found throughout the pond- attached to the sides, bottom, and the gravel- but most live in the filter medium, due to the great amount of surface area.
Nitrite, although less toxic than ammonia, can kill fish if the level is high enough. Nitrite is converted to nitrate by another friendly bacteria called nitrobacter. Like the nitrosomonas bacteria, these live primarily in the filter medium. High nitrate levels, especially long term, are detrimental to the pond environment and the fish. In the normal, balanced pond, nitrate is either removed from the pond by partial water changes or used by plants and algae as food.
New Ponds: The nitrifying bacteria- the nitrosomonas and nitrobacter- need time to reproduce and establish themselves in a new pond in order to handle the big load. A brand new pond does not have sufficient nitrifying bacteria to support more than a few small fish, so only start a pond with small quantities. PATIENCE in adding new fish MUST be exercised to avoid deadly ammonia or nitrite levels. It normally takes anywhere from 4 to 8 weeks for enough nitrifying bacteria to develop. Test kits should be used to monitor the ammonia and nitrite levels in newly set up ponds.