Perry,
Sorry about your loss. What kind of puffer was it?
My wife and I have had
Green Spotted Puffers. We bought 4. Slowly, one by one, they died off, water parameters were perfect. Then my wife started searching the net and found wetwebmedia.com. Over the next few days we learned quite a bit about the fish we bought. It seams that GSPs can be pretty hard to keep. Stress and parasites are a few of the leading causes of the high mortalitly rate.
We noticed that a few days before a puffer died, it's belly would turn from white, to a light shade of grey. The belly would progressively get darker, almost turning a dark charcol color before it died. We had one puffer out of the original 4 that made it, Hunk. We eventually moved him into a 44 gallon tank with hopes of eventually converting him to salt water. We were breaking our 10 gallon tank down and put the rubber lipped pleco in the 44 gallon tank. I never saw the pleco after we put him in. A few days later, and I constantly kick myself for not noticing it sooner, Hunk was COVERED in ick. Puffers are scaless fish and can't handle the usual copper medications. About 3 days after noticing the ick and trying everything I could think of, Hunk died.
To this day, my wife refuses to get another GSP, because Hunk was her favorite fish and it really hurt her when we couldn't save him. We had him over a year.
Check out the brackish section on wetwebmedia, there's a ton of good info there about puffers.
Kevin