g.head - Your copper build-up question has no one answer for every pond. It will vary from pond to pond and region to region. Generally speaking the lower the water hardness the quicker Cu build-up will be a problem. It will also depend on how aerobic your sediments are. As I understand it, the more aerobic the sediments are the more likely the copper will dissolve from bound or stable state out of the sediments. There has not been a lot of published research on this topic that I am aware of.

The amount of copper a pond can absorb will also be dependant on its size (pounds Cu /acre). Sediments have the ability to absorb a definative amount of copper. Once that level has been reached the where can newly added doses of Cupper go if the sediments are saturated?

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management