I have used Cutrine-plus for years without a single problem. But, I follow the label explicitly, know the target species and understand how it all works. Be a good student, know your plants, and the product will work. Regarding grass carp, they won't eat algae. Can't bite it.
A key thing to remember here, treating plants only deals with a symptom. Plants need three factors to grow...sunlight, food and temperature. Grass carp only act to eat the plants, convert vegetation to nutrients, then re-introduce it to the system. More food for different plants, until flushing rains send those nutrients downstream.

Teach a man to grow fish...
He can teach to catch fish...