Sudden Comet Deaths

Question
I have a total pond area of 10,000 gallons, with the my bottom pond being 8,500 gallons in total.  I have 50 Comets and 4 Koi.  BioFall,skimmer, the works...

All water tests are within normal limits.  Water is clear and healthy; plants growing and thriving, fish are seemingly healthy and putting on weight.  I have had them almost 2 months.  It seems like every few days, we find a couple of Comets dead.  There is no sign of trauma or
disease.  They literally look perfectly healthy.

Do you have any thoughts as to what may be happening?  My fiancee and I spend hours a day at the pond, just enjoying it; relaxing beside it and watching our fish "children."  We see no signs of aggression in any of the fish.  The Koi almost seem to "parent" the smaller Comets.  The Comets eat a healthy diet and swim around vigorously.  Then wham...we
find a couple dead.

Any suggestions?

Answer
Hi Heather,
Thanx for your question.  How new are the comets?  If they have been recently introduced, they may have suffered some kind of trauma during introduction.  Personally, though, I think the koi are bullying the fish and you just don't see the behavior.  Koi can be very aggressive, especially with smaller fish.  If they are chasing them around and you don't see it or don't realize they're doing it, they are probably wearing you comets out.  What may appear to be parenting is probably aggressive behavior that is frightening and wearing down the fish.  I hope this helps.
Tom