The cutrine should be diluted around 9 to one with tap water and sprayed on the surface of the algae. Once a month often isn't enough. Algae can return in as little as a week.

Sounds like to long of an interval between treatment and perhaps incorrect application techniques to me.

A gallon of cutrine costs less than $30, and a 2 gallon sprayer should be less than $20. Perhaps you should forget about the water department and have at it yourself. Be careful and watch for signs of low DO if you treat it all at once. Keep the aeration going.