In a healthy established tank odors are not normal, its a sign of a problem.
In a newer tank it may not be as indicative of a real problem, but more often just the new system still in flux, e.g. a bacterial bloom, excessive nutrients or some such.
In your case, I'd say that after a month running established media, it is time to clean the filter/media.
Using a bucket of either tank water or treated tap, rinse the media very well, don't be gentle, get all the crud out of it, you won't dislodge beneficial bacteria.
Rinse the filter box out well.
Also, any leftovers from a SA Puffer's ideal diet (meaty foods), is very likely to end up in the substrate and contribute to high levels of dissolved organics in the water.
Though I usually don't recommend carbon in filtration, it may be a good option for you. It will absorb the organics/odor, but will require changing weekly/biweekly depending on bio load.
What make/model of filter are you running?
What medias are you using in it?
If you use substrate, what kind, how deep and how often are you vacuuming it?
How big are your Puffers?