coral_hog;579466 wrote: What you are seeing is the very end of the Nitrogen cycle..., or basically, anerobic bacteria converting nitrates to nitrogen gas. It is usually more obvious if you have a DSB. The nitrogen gas collects together in the sand bed until a large enough bubble builds up, and breaks through the surface.
jrob11111;579696 wrote: Dumb question, but DSB = deep sand bed?