Question

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Followup To

Question -
About 40 koi in the pond.  The fact that eight have died tells me
they've all been compromised.  Assuming we get oxyen levels
back up to 8ppm or more, what can we do to revitalize the koi
that survived?

Answer -
Hi,
I would put a large air stone in your pond to put oxygen in the
water and also do a partial water change, not knowing what
caused the problem that is all I can suggest.
George.

What is an air stone?  Why would we change the water?  Is it
possible that the copper sulfate can somehow poison the pond
even after it has caused the algae to die off?  We had the use of a
large fountain for several days and brought the oxygen level up
to about 7.  However, the fish don't respond to food pellets like
they used to.  Is it possible that the koi and catfish's brains have
been affected by loss of oxygen?  If so, is there anything we can
do to help them now?  Len Belzer

Answer
Hi,
An air stone is a stone you put in your pond and pump air through it to oxygenate your pond similar to the ones used in aquariums only larger,copper sulfate is  deadly if you do not use the correct dose and the only way to get rid is, as I said before, water change and continually water change until  all trace as gone.
Sorry that I cannot be more helpful.
George.