I have some smallish pebbles in my tank, been in there for a month or so now. I've noticed they are turning a dark blue/grey kind of colour on the bottom, which stains my sand all the way to the bottom. I was removing the pebbles when I found eggs laid on them (have another thread regarding those 
). Just wondering what was causing this? Is it a mould or something? I did the vinegar test and boiled them before putting them in.
Thanks
Lee
). Just wondering what was causing this? Is it a mould or something? I did the vinegar test and boiled them before putting them in. Thanks
Lee
