Copper needs another metal in alloy in order to be a biocide ... according to the research I did a few years ago. Antifouling paints used to have zinc added to them for the same reason. Kinda makes sense because copper-nickel pipes are used in ships. Also thru hulls are not copper. They are a copper alloy (bronze).
>From the internet forums, it seems copper is not an effective algaecide. I have heard of some sailors mixing in a bag of tetracycline (livestock antibiotic) into the bottom fouling mix. They claimed improved performance. .... Fish in the area are not getting sick now either (humor)
regards,
tim
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