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re how much cu is toxic?

Thank you Stephan, you helped me a lot!

Stephan wrote:
> Repeating what others have already replied: the answer depends on the
water conditions and the species in question. Hardness and chelating
organics in the water will reduce toxicity.
> >From experience I can say that plants which tolerate a high copper
content include most Echinodorus, Crypts, Anubias, Hygrophila, Microsorium
and Lotus. Mosses and of course red algae are sensitive. Tetras are included
with species of fish which tolerate high Cu levels. Otos do not like high Cu
levels. Corys and livebearers are said to be very sensitive.
> Snails, shrimps and other invertebrates are especially sensitive.
> I use copper occasionally to kill any red algae that appear in my tanks,
with a syringe of concentrated copper sulphate solution dosed directly on
the algae. I do not have sensitive organisms in my tank except snails and
moss. I know when the level of copper has become toxic when the snails
retreat into their shells and start producing mucus strings. When this is
noted and copper dosing is stopped and the moss is not be effected.
> I would therefore suggest that snails be used as indicator organisms for
copper toxicity. If freshwater snails (eg ramshorn) do not act strangely
when put into the test water (ie staying withdrawn, releasing large amounts
of mucus) then the water is safe!