can you swim in a pool with algae?
The answer to this question is it depends. Pools with algae can be safe to swim in, but it depends on the type of algae and the amount present. Algae can produce toxins that can be harmful if ingested, so always check with your local health department before swimming in a pool with algae. If there is a lot of algae in the pool, it is recommended not to swim in it until it can be treated.
Algae are simple plants that require sunlight and water to grow. These green or blue-green slimy pools of slime form on top of or in your pool when conditions are right for growth, but visible algae is not always present, especially if you have a sand filter. Sand filters work by allowing water to pass through the sand and trapping dirt and debris in the process, but an accumulation of dead algae cells can also be trapped inside your sand filter. When these cells come in contact with chlorine, bromine or biguanide sanitizers found in most pool supplies they are broken down releasing phosphates. Phosphates provide the essential nutrient for algae to grow, so if you have high levels of phosphates in your pool water it will create the perfect conditions for algae to grow.
There are several ways to test for phosphates in your pool water. You can purchase a phosphate test kit at most pool stores or online, or you can collect sand from your sand filter and bring it to your local pool store for phosphate testing.