Co2 Day Two: Three fish crash and burn!

Okay, so I got my CO2 equipment "working," and had it set to release
about 50 - 60 bubbles per minute on a ten hour cycle timed with the
compact fluorescents.

Yesterday went fine. Today, around 6:00 pm (8 hours into the timed
cycle) I noted three fishes were head-first in the plants at the
bottom of the tank and still alive but breathing heavily: a small
dwarf rainbow, and two Madagascar rainbows...

Now, this has to be something to do with the CO2 because I rarely lose
any fish in this tank. So I immediately switched off the CO2 and am
hoping that somehow the fishes will pull through.

I checked the Ph and did not note any substantial changes or a
"crash." Are these particular fish just sensitive to the extra CO2?
Any ideas on where to go from here? I was thinking I'd start again
with the unit on for an hour or two a day, and gradually increase the
amount of time it is on so that the fish can adapt more gradually.

Any thoughts would be appreciated,

-Andy