Hydrogen sulfide

H2S requires an oxygen void environment with lots of organic waste for anaerobic bacteria to create. In a fresh tank I highly doubt you've had enough time and deep enough sand to facilitate this happening.
Information such as tank age, water parameters, equipment setup and pictures would greatly increase a persons ability to accurately diagnose what it could be.
Like was said above, more than likely it was just O2.
Good Luck

 

Sorry guys don't have a camera its coming this month.