On May 5, 4:27�pm, Oren wrote:
On Tue, 5 May 2009 05:45:07 -0700 (PDT), bob haller
wrote:

On May 4, 9:25?pm, Red Green wrote:
"scorpster" wrote :

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.

Pressure washer.

pond stores sell algea killer stuff.

use with care.

OP could consult an Ichthyologists, or just borrow a book from a
library on garden ponds and water gardens.

nature is sometimes best left natural

No work, no fuss, no hazard to fish...........

basic ignore algea.