Hello I have a water feature with many waterfalls and a pond at the bottom.My husband built it. He made the pond so the grandkids could wade in it.He died 3 years ago and the pond is suffering! I don’t have a clue how many gallons. The pond is about 15’ X 10’ but he put crates in and dug trenches so the water below wouldn’t freeze. I have algae and I was using chlorine powder but it left a white film. I need to know what works on algae.