I just came across this at Koivet, is it a possibility?
Second paragraph - they have not seemed to be sick. Joann
snip
Black Spots Appearing
Some little black spots are called Shimi. This is an unfortunate
genetic defect in some fish wherein a Kohaku gets some little black dots and
they're suddenly a worthless Sanke. There is also a growing body of evidence
that suggests the condition may be common in water with high turnover or
exposure to caustic irritants like Chlorine. Case in point: Shimi is rarely
noted in natural greenwater ponds but is common in crowded manipulated reuse
systems.
Another type of blackening is a generalized type wherein the fins and
body may develop a blackening change from chronic or caustic trauma. Case in
Point: Fish are badly ammonia burned by a filtration failure or
inadequacy --- A week later, after water quality is restored, the fish
develop blackened areas, called a Melanophore Migration. Severe parasitisms
can later cause blackening as the skin starts to heal. The blackening is not
permanent, but may remain for two to four weeks before subsiding.


"FBCS" wrote in message
...
Ingrid help, anybody else can jump right on in with suggestions.

I noticed some of my GF have black in their gills (inside). Is it
something
to be concerned about. I have tested the water and all seems fine. They
look
fine none are wacking out. None of my Koi have this. I never noticed this
on
them before last week. What made me notice was one of my ugly black GF
that
I thought was gone showed up a pretty red gold then I noticed the black
inside the gills thought it was his coloring then I noticed some of the
others had the same thing. I have read about gill damage, is this it?
Joann