Cu is supposedly not bioaccumlative, although it is on at least 3 government agency lists as a hazardous chemical. when bound it does not decompose and is a stable compound that eventually deposits in the sediments. In the sediments it can redissolve under certain sediment conditions or chemistries.
Different species of fish have different sensitivities to copper ions in the water. With trout and minnows being most sensitive, LMB as pretty tolerant and most other species somewhere in between. Most fish fry are pretty sensitive to applications of Cu strong enough to kill algae, usually 1ppm. Traditional application methods for CuSO4 results in uneven concentrations of Cu as it is distributed. Cu ions quickly become chemically bound or absorbed and inactive in most all hard water applications (total hardness >100mg/L, ppm).
Application of 20 lbs of CuSO4 per acft is 7.4 times the recommended application rate of 1ppm. Often FA is just around the pond perimeter thus treating that depth zone is the most responsible application method. When treating FA in a pond, generally the entire water column usually does not need to be dosed at 1ppm. Actually copper sulfate applied to a pond surface often does not penetrate the water column deeper than 2 - 4 ft due to the chemical binding forces of the positive charged copper ions in the water column. Copper is a contact killer thus direct application of copper solution on the offending algae is often the best treatment plan.
Good info, I should clarify my previous comment, in regards to fish kills, my understanding is that 20lbs/acft is maximum label rate and should never be exceeded.
