You can have the bands as close as you like, but note that they may overlap (affect each other), depending on the bandwidth settings. If you have bands at 80 and 81 Hz, they will be pretty much identical, and you could instead just have a single band with a combined gain value.
An equalizer would usually have its bands evenly spaced (logarithmically), all with the same bandwidth value. Note the bands are 1 octave apart in the example code I linked above.