This may be true by definition but one product does both jobs. Invisible algae sounds like a contradiction but, in fact, thousands of algae are growing before they become visible in an algae bloom. Algae can be filtered out of water. Generally, if you can see it, you can filter it. Algae doesn't grow in cold water.
Temperatures have to drop to near freezing before algae move into a dormant state.
Studies in the Arctic Circle indicate that as long as light is present algae will grow. Algae doesn't grow in low pH water. During periods of hot weather and intense sunlight, photosynthesis is at its peak. Algae doesn't grow in cold water. Temperatures have to drop to near freezing before algae move into a dormant state.