The algea will bloom this time of year because the sun encourages the growth and the warmth inside the waterer does as well. It comes on fast in the plastic waterers and I keep jugs of white vinegar on hand and rotate the waterers to soak one while the others are being used. I add a little Clorox too for the tougher ones to kill anything other than algea. The fact we have hard limestone water in MN also creates a lime build-up when the water gets warm, or some days in July, hot. So, even using bleach alone will not remove the lime deposit, which is the reason for the vinegar. And if you are afraid of using bleach in the waterers, to prevent some problems like thrush (a fungal infection that can be contracted from dirty waterers/feeders), it is recommended to put about a teaspoon of bleach into the drinking water per 5 gallons of water. Metal waterers don't get that growth, but they get other sliminess if/when poop gets in them, especially on warmer or hotter days.
I soak waterers overnight and using a brush, by the next day nearly all the build-up will easily brush out, sometimes even just a sprayer will get it off, depending how long you go between cleanings.
