Please choose the correct ending to complete the given sentence: Home and Garden: [header] How to get rid of blackspot algae in your swimming pool [title] Understand black algae. [step] Like any alga species, black algae (which are really blue-green algae that look black) will grow quickly in warm water on a sunny day. Black algae are chlorine-resistant, because they have a protective outer layer that makes regular sanitization ineffective.

Ending1: [title] Try a plastic or glass aquarium pump to see if you can get rid of the mildew. [step] Plastic pumps don't scratch or dry algae scales, making them great for water-decontamination, while glass pumps may not. Ending2: While algae aren't harmful, their presence can be a sign that other bacteria are present. [substeps] Other alga species that are common in pools are green algae, mustard or yellow algae, and pink algae, which is actually a bacterium. Ending3: [substeps] No matter the weather, a change in water temperature is advisable. Because of this, you should still be cautious when swimming in a pool with black algae. Ending4: Black algae can also grow up in clumps on your pool floor and around corners, which can aggravate the entire problem. [substeps] Remove black algae by using a commercial water purification spray.

Answer format: ending1/ending2/ending3/ending4