Phosphorous, like nitrogen, is an essential nutrient for the plants and animals that make up the aquatic food chain. (Phosphorous cycles through the environment as depicted in the illustration below.) However, phosphorous is generally found in short supply in fresh water systems. As a result, even a modest increase in phosphorous can trigger accelerate plant growth, algal blooms, low dissolved oxygen, and create unlivable conditions for certain fish, invertebrates, and other creatures.

Phosphorous from natural sources, such as forest fires and fallout from volcanic eruptions, is insignificant when compared to human-caused enrichments. Phosphorous is introduced into the environment from human activities such as human and animal wastes, fertilizers, industrial wastes, and human disturbance of the land and its vegetation.

1. Fill the test tube (0106) to the 10 mL line with the water sample.
2. Add one Phosphorous TesTab (5422).
3. Cap and mix by inverting until the tablet has disintegrated. Bits of material may remain in the sample.
4. Wait 5 minutes for the blue color to develop.
   NOTE: If the sample does not develop a blue color (sample is colorless), record the result as 0 ppm.
5. Compare the color of the sample to the Phosphate color chart.
6. Record the result as ppm Phosphate.

• 1 ppm Excellent
• 2 ppm Good
• 4 ppm Fair

Phosphate levels above 0.03 ppm can encourage growth of plants and algae in aquatic systems. High levels of phosphate can lead to overgrowth of plants, increased bacterial activity, and decreased oxygen levels.