There is a lot of tolerance variability between species of fish and shrimp. I looked into this some time ago and came to the conclusion that a value above 35ppb (Parts Per Billion). is pushing it for fish and shrimp. but others have come across data with LD 50 values above this. I have not seen any aquarium fertilizer with more than 10ppb of copper in it. Most have less than 3ppb. Some fertilizers don't have it at all even though plants will not grow without it.
However all that said you shouldn't be worrying about your fertilizer. You should be worried about your tap water. Legally the maximum copper level allowed in US drinking water is 1.3ppm. 90% of the copper in drinking water comes from the corrosion of copper pipes in homes. I have always used RO water in my aquariums. But recently I did test my tap water and found I have 50ppb in my tap water. Copper piping has been standard in homes for at least 50 years. Given that most aquariums are filled with tap water it is likely that shrimp can handle more copper than most people expect.
However all that said you shouldn't be worrying about your fertilizer. You should be worried about your tap water. Legally the maximum copper level allowed in US drinking water is 1.3ppm. 90% of the copper in drinking water comes from the corrosion of copper pipes in homes. I have always used RO water in my aquariums. But recently I did test my tap water and found I have 50ppb in my tap water. Copper piping has been standard in homes for at least 50 years. Given that most aquariums are filled with tap water it is likely that shrimp can handle more copper than most people expect.
Maybe I should use a trace with less copper to start with.
