"Nikki Casali" wrote in message
...
John H. wrote:

Hi, I was doing a water change for my 60 gal planted tank (florite/gravel
mix) and while I was cleaning the gravel, noticed
a lot of bubbles being liberated... is this CO2 ? O2 and shoud I be
worried about it?

It could be either O2 or hydrogen sulphide (H2S). H2S is deadly. If you
noticed a rotten egg smell when the gas was released, then this was H2S. I
have large O2 bubbles created by the roots of my plants. These
periodically force their way up through the gravel to the water surface.
This is a good sign. On the other hand, areas of gravel that remain
undisturbed and are not aerated for long periods of time promote bacteria
that become anaerobic. These areas in my tank become black. I can only see
these when they are up against the glass. When they are finally
disturbed - gravel cleaner, fish digging etc. - they release bubbles that
smell like rotten eggs. I have heard that if fish get a big enough waft of
H2S it can can kill.

I think this is more of a problem with sand substrates, where the sand can
get compacted. Allowing plants to grow completely across the substrate
should help prevent that as the roots produce O2. Maybe you simply have O2
bubbles being produced by the roots?

Nikki

Yes Nikki, I believe they are O2 also. There is no rotten egg smell at all.
Most of my plants consists of that fast spreading grasses and the roots are
thick...
Thanks for the help!