These leaves (also known as Indian Almond leaves) produce tannins that darker the water (like a cup of tea). While some people don’t like the look of the darker water, it’s healthy for the fish. The water should be changed on it’s normal schedule and they are filter safe (although some filters will remove some tannins). These leaves are great, but this is very overpriced. You can get a very large pack for $10 on Amazon.