Good to hear your puff is okay... but to answer your question about puffing, some puffers do just puff randomly as if they were "stretching", or sometimes its due to stress etc...
But as most have mentioned here nitrates as high as 90 is really too high for a puffer, since they are scaleless fish... either way, i'm not here to knock you down, just wanted to let you know some small facts about puffers and puffing...
Eitherway, good luck with your puff and hopefully it will hold out till you get your 90G setup...