closed cycle pond question

I got in a big arguement with my neighbor last night. He has seen my
Koi pond and has decided that he wants one too. He found a contractor
who tells him he can install a 1000 gallon Koi pond and waterfall that
can support Koi without the need to feed them. The Koi will live off
the plants and algae. The contractor told him my pond was all wrong
because I had to feed my Koi and this led to occassional mildly cloudy
water. I think my neighbor is getting fed a line of BS. The
contractor charges a fortune. Oh yea, the contractor told him he
would have to make the pond out of granite, it is the only stone with
stable PH. My neighbor says that he hired a "professional" and I did
my pond myself.

Is there any truth at all in a 1000 gallon closed loop bio-pond for
Koi??

Doing a slow burn

Dave