- First I noticed the color was less intense
- Two days later I noticed the puffer was constantly hiding
- Two days later I noticed the puffer, when out and about, was completely listless and mindlessly bumped into things, but still swimming upright. I also noticed redness in the gill area, but wasn't sure if it was because the less intense color was allowing me to see through the skin slightly.
- Two days later dead fish
On the second day I tested my water parameters and came up with the following:
- Ammonia: 0
- Nitrite: 0
- Nitrate: 10-20 mg/L
- pH: 8
- sg: 1.003
On the fourth day, becoming frantic, I dosed the entire tank with Prazipro and Seachem Prime. The symptoms mostly lineup with ammonia poisoning, but only my puffer was affected so I wasn't sure. I also know that puffers can suffer from internal parasites (even though I didn't see any physical symptoms) and Prazipro being a relatively gentle drug, I decided to try it as a last ditch effort.
The only thing I can think of is that I changed my water changing schedule from every week to every month. Last weekend I did my first water change after a month of no water changes, and I decided to wash out my sponge filters (not biological media). I tested my nitrates every week during the month and they never exceeded 20 mg/L. The only thing I can imagine is that somehow I caused an ammonia spike (no idea).
If I had to go back and do it again, I would probably start by doing a water change once I saw the coloring was faded. I'm still not sure what happened though, and would hope to get some insight from your past experiences with puffers.