Cutrine Plus Algaecide can be used in ponds and lakes to help control different types of algae, except if you have trout, koi fish and hybrid goldfish, Cutrine Plus Algaecide is toxic to these types of fish. We recommend to treat 1/2 of your pond first and wait 14 days to treat the other 1/2 of the pond to avoid fish suffocation caused by oxygen depletion from decaying algae.
We do not see anything on the Cutrine Pus Algaecide label that says it is unsafe for carp or anything regarding water hardness. It does mention that trout could be harmed if the water is too soft or acidic. There are a few different ways to go about testing your water levels so you may want to just google a few options or videos to see what is easiest or best for you.
Cutrine Plus Algaecide is only labeled for controlling algae, we are not aware of any other off label usages such as control of bugs.
The typical dilution range of water to Cutrine Plus Algaecide is 9:1 when using a backpack-type sprayer ( 1 part Cutrine and 9 parts water).