Sand (toxic gases)

once a week is what I heard

Are you going to plant it? If so, that will help, especially plants the develop large rootmasses, like swords. Otherwise, IMO, you'd be better off stocking it with an aquatic worm that will do the work for you--black worms, maybe? There are a few species out there. The problem is not that stagnant areas will develop, but that will be disturbed after developing. The digging of the puffer should prevent much of that, especially if he's encouraged to root around for critters.

I have a tank with sand, and two inhabitants (stingrays) are stirring the sand all day long, so getting somkeone to do the work for you is better.

Another poster gave me the advice of:

Take a clothes hanger and straighten it. Use the hanger to run through the sand, it does the same job and makes less of a mess.

Once a month or so should do it. The gases are really created by bacteria that feed on decaying matter and a good monthly swirl in the sand will prevent the build up. It takes time for the gases to build up to a dangerous level so usually you only hear about this from someone who neglects sand maintenence for a long period of time.

Stirring will also put the detritus under the sand...If you DON'T stir the sand, then there will be very few organics there to promote the growth of anaerobic bacteria in the first place. Small grain substrates seldom have much of a problem with organics making it very deep--other than the digging action of the puffer. He'll likely pick a preferred spot to dig, keeping that spot well stirred, and the rest of the bed will be stable. Stirring it manually requires consistancy, and removing all detritius from the surface before disturbing the bed--more of a pain, IMO.