Re: Bubbles in the gravel

In a recent post there was a comment about bubbles being visible in the 
gravel.  This is common for me where the tank gets natural light.  The 
area on the glass under the gravel gets a very dark algae buildup that at 
times forms large bubbles.  I would suspect these are not H2S but O2 
since these tanks also have UGF.  I have no equipment to suck out one of 
these bubbles and analyze it but it would be interesting if one of the 
real experts on the list would take on the project.  The tanks where I 
observe this are all doing very well.  It is a reminder that gravel 
vacuuming should be done more often but in one tank the val is crammed 
together against the natural light side of the tank and the below gravel 
black looking algae is thick and full of bubbles.  Black is a subjective 
color description - very  very dark green would also describe the algae.

OTOH, if stirring up gravel away from the light exposed edges produces 
bubbles then I would be concerned.  Also, smell is a good indicator.  
Rotten egg smell (H2S) is bad news.  

--Earle Hamilton from northern Michigan where coral once grew