Ever since I read somewhere on here about giving your birds Apple Cider vinegar, I've searched for the unfiltered one with no luck. But I have a 7 gallon waterer and when I fill it, I rinse it out with water first....and then add about a half cup of the vinegar. It stays very clean and no algae growth. And here down in the sunny south, algae growth is a big problem. To me it's a cheap and painless remedy...sure beats scrubbing down the inside of the waterer.
Kurt
Kurt