Pond buildup is a common problem caused by the accumulation of ALGAE and SCUM. ALGAE, which is a five-letter word, is a type of aquatic plant that can grow in large numbers and cause water to become murky. SCUM, a four-letter word, is a thin layer of organic material that forms on the surface of water and can contain bacteria, fungi, and other microorganisms. Both ALGAE and SCUM can contribute to pond buildup, leading to an unhealthy environment for fish and other aquatic life.