The Effects of High Phosphate Levels on Saltwater Fish

For people who raise saltwater fish as a hobby, high phosphates mean algae and algae can mean problems in your fish tank. It can also mean problems for saltwater fish in the wild. Phosphates can come from a variety of sources, such as fish feces, pH buffers and uneaten food. Try to keep your phosphate levels at .2 mg/L or lower to control algae. Partially changing the water in your fish tank more frequently will help do this.

  1. Increased Fish Population

    • Phosphorus is necessary for plant and animal growth. Phosphorus can be found in phosphates. When phosphates begin rising in a water source, the amount of plankton and water plants in the water increases. More fish move in the area because it has become a richer source of food.

    pH Buffer

    • Phosphates contribute to alkalinity. The greater the phosphate level, the greater the alkalinity of the water. Alkalinity helps buffer the pH of acidic water by absorbing the acids in water. This absorption helps protect fish against the affects of acid in the water, such as acid rain. Saltwater fish generally prefer water that is alkaline (the pH is above 7.0) and at a pH of about 8.3, according to A World of Fish.

    Fish Deaths

    • Too much phosphate in the water causes a problem for saltwater fish. It encourages algae and other water weeds to grow. These plants use up the oxygen in a body of saltwater and either kill the fish within the region or drive them away because there is no food source. This area is called a dead spot because it cannot support life.