Cleaning concrete pond edges without affecting fish?

We have a concrete pond with fish, and the concrete liner that is exposed to the air has some black algae stains from when the water level used to be higher. The new permanent water level is below the stain. What would be the easiest way to clean the dried black algae without killing the fish? For example bleach would be great for cleaning a white surface, except I think that would kill everything.
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Pressure washer.
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pi068.nbdc.sbc.com:

pond stores sell algea killer stuff.
use with care.
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wrote:
in

OP could consult an Ichthyologists, or just borrow a book from a library on garden ponds and water gardens.
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nature is sometimes best left natural:)
No work, no fuss, no hazard to fish...........
basic ignore algea.
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checking with a local aquarium or pond club or his neighborhood fish store.
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