dsb clarification

Some of you had recommended a dsb for lowering nitrates and i said the lfs
told me not to. I said something about nitrogen bubbles and... well i'm a
nubee and was basically talkin' out my bottom and this is what the lfs said.

Paraphrase: They only recommend 1" of a sand bed "on small tanks" due lack
of real-estate. He didn't say anything about borrowing animal releasing the
bubbles he said the borrowing animals "rasps" could expose the anaerobic
bacteria and cause the ammonia to spike in a dsb. He did say something about
nitrogen bubbles but i don't remember the context.

I'm learning. Sorry for the confusion

I'm considering a dsb in my 45 gal tall tank as it has room. How many inches
do you suggest?

Jim