Is you gravel the black 'coated' kind? If you are maybe it's just flaking
off.

I have used Sera Floredepot in my tank with great results. With CO2, I've
never grown an Echinodorus 'Ozelot' as big as then.

"Wynand" wrote in message
...
is that of the gas bubles from the substrate
(usinfg sera as the bottom gravel)
above normal