I was away on vacation for 1 1/2 week during the Easter. Right when I was about to leave home (I had even put my dog into the car, and was just checking of all the lights were turned off and things like that), I saw that the filter in my salivator tank didn't work. This is an internal Sera filter (I start to hate those filters too. I get more and more against Sera filters on the whole), where the sponge is attached to the pump, and there's nothing covering the sponge. Usually when there's problems with internal filters, there's either dirt on the impeller (if they don't work at all), or there's the sponges being very dirty. So I tried a quick fix. There was nothing wrong with the impeller (the pump did work, but the water flow was very, very poor). I tried to rinse the sponge. When I do this with a Sera filter, it always releases an awful lot of dirt when I start the filter again. Even with the very, very poor water flow, this happened this time too. The whole tank went very cloudy. I tried the pump without the sponge, and the waterflow didn't improve. It was barely pumping any water at all. And now the water in the tank was bad too. With the knowledge of the puffer's sensitivity to the water quality, I just had to make a quick water change (about 30 %), even though my dog was waiting in the car, and then I just had to leave the filter like it was, as I was several hours late already. I was very, very afraid of what would find when I came back. (I also found nitrites in another tank too, where I have my absolute favorite fishes. Argh!) I've never felt so bad leaving my tanks before. With so bad filtering (if I turned the outflow in the surface, pointing against the roof, the water managed to flow about half a centimeter away from the pump - that is very, very bad circulation! Even the weakest pumps I've ever had, has been better than that! With almost a non existant filtration and lots of rotting material spread in the water, it would surely be too much for a puffer to make it.
But believe it or not: when I came back 1 1/2 week later, my salivator was
still alive. The filter was still working as bad as it did when I left, which means almost not at all. You can barely feel the flow if you put your fingers in front of it. I've now put in an extra filter, which only is suitable for a tank size up to 45 litres (and the tank is a 85 litre), and that was just soooo much more powerful than the one that didn't work. The difference is very big! I have no idea how my little Jack the Ripper made it through my vacation, but he did! So did the fishes in the tank where I got nitrite readings the same day.
I just had to share this story, to tell you all that puffers
can survive bad conditions. All though I would never, ever like to put a puffer through something like this again. I would have expected certain death in an almost not filtered tank, full of dirt in the water. But he must be a fighter, this one, my beloved Jack the Ripper!
I can't blame anything else than my own clumsyness! 
I had to use cruches the rest of the vacation, and couldn't be with the others when they went outside. 
Except that I got some nice birthday presents (a bit late), and a birthday dinner (which I usually never get, living by my own).
But I am happy to finally have a salivator that I can see!