some info on copper From Merck Veterinary Manual,
http://www.merckvetmanual.com/mvm/in.../bc/170404.htm
Copper sulfate (CuSO4) is not approved by the FDA; however, a number of compounds containing CuSO4 have been approved by the US Environmental Protection Agency (EPA) as algicides for use in aquatic sites. CuSO4 is currently designated as “of moderate regulatory concern” and is used in food fish practice; however, practitioners must keep themselves informed of possible changes in the status of this chemical. CuSO4 has been used for many years as a parasiticide and is particularly useful in large production ponds because of its relatively low cost. Copper is highly toxic to fish, and safe use depends on its interaction with carbonate salts in water. In freshwater systems, the concentration of CuSO4 applied should be based on the total alkalinity (TA) of the water. If TA is <50 mg/L, copper cannot be used safely without performing a bioassay. If TA is 50-250 mg/L, a safe concentration of CuSO4 can be determined by dividing the TA by 100. For example, if TA = 100 mg/L, a safe concentration of CuSO4 would be 1 mg/L. If TA is >250 mg/L, the concentration of CuSO4 should not exceed 2.5 mg/L. Other concerns when treating a pond with CuSO4 (in addition to its direct toxicity to fish) relate to its algicidal activity. Rapid death of an algal bloom can precipitate a catastrophic oxygen depletion. Use of CuSO4 in ponds not equipped with supplemental aeration is risky. Use of CuSO4 is hazardous if a pond has a heavy algal bloom (secchi disc ≤18 in.) or if the water is already deficient in oxygen due to other factors, (eg, cloudy weather or high water temperature). CuSO4 is efficacious against most protozoal parasites, is economical, and despite these concerns, may be an excellent choice when multiple treatments are required (eg, in an epizootic of Ichthyophthirius multifiliis ). In saltwater systems, copper is sometimes applied in a chelated form because it stays in concentration longer. Chelated compounds may be difficult to use safely and require careful monitoring. CuSO4 can be used to treat marine fish, but the concentration of active copper must be closely monitored (test kits are available) and should be maintained at 0.2 mg/L for up to 3 wk. Safe and effective use of copper in marine systems requires that Cu2+ concentrations be tested at least once a day. Copper is extremely toxic to invertebrates, so these must be removed before the water is treated. Copper is also toxic to plants and should not be used in ornamental ponds that have been stocked with valuable plants. Finally, copper will impact bacteria in biofilters and a transient increase in ammonia should be expected for several days following treatment. Monitoring ammonia until measurable concentrations subside is recommended.