dead goldfish

Question
I have an outdoors fish pond the size of a bathtub.  The 5 original goldfish have breed and I have 20 2" long babies (they are now months old).  Over the past two months I have gone away 3 times overnight camping and each time I have returned there has been 1 dead baby goldfish.  Before leaving on the Sat morning I feed them and they are all healthy and fine - Never any sign of a fish being sick.  Any suggestions as to what could be causing 1 fish to die.

Answer
The things that typically kill fish outdoors are:

Disease: bacteria, parasites, fungus

Poisons: fertilizer, insecticide, etc.

Improper water chemistry: ammonia, nitrate, low pH, etc.

The first thing to check is your water chemistry.  Most pet stores will do this for you.  Sometimes adding a little bit of salt to the water will help your fish withstand more stress.