Last summer I used the water protector and didn't have any scum. This summer I had planned to sell the chickens but life and my wife got in the way, so they're still here. I just finished washing scum from the waterer and once I post this reply I'm going out to put Manna Pro Water Protector in it. I don't like buying tiny little bottles at high prices so I'll be searching for a better source but I'm not tossing out a watering system that works year around without dripping all over the coop floor for one that will.