lady who sits nearby shouted out "I don't know about her pond, but SHE needs
to get a life - she's actually upset about some of her fish dying!"

Sounds like someone needs to go to sensitivity traning. Sheesh.
You should have heard me threatening K30 this afternoon regarding taking
some of my frog spawn, not to leave it in the car! Shameless Am I.

Just as an added note, the dead fish
did not die in a pretty state. They all had blood in their fins and some
areas of their bodies, and the fins were all frayed and tattered looking.

Usually there is ammonia before nitrite, and the above sounds like serious
ammonia happened. Perhaps by the time you noticed a problem and checked it
the ammonia had converted to Nitrite.

Even a continous low level of ammonia can be stressful, as I found out last
year, when I hit Critical Mass. Now I have plenty of ammonia detoxer on
hand, and started testing my water early on. I've had one test show an
inkling of ammonia after I started the filter, so I treated it, so far so
good now. I have 5 fewer fish than last year at this time, so I should be
good. If I have trouble I've already picked out who gets sold.

Very important to have the treatments handy and fresh test kits, that you
use.
~ jan (Do you know where your water quality is?)