That rock isn't good. It will leak calcium into the tank, and raise the Ph, eventually kinng the fish! I would take it out!
Yeah, i thought it would buffer the PH until i tested the tap water and it is PH8 anyway so just left it in. Didn't realise it would leak calcium. Might take it out then!
8.0! That it high! I doubt those neons will like it that high! The Ph inside the tank is most likely going to be at least 8.5, and although adaptable, neons will prefer a lower Ph (7.5-6.0ish)! I recommend taking that rock out asap. Besides, it doesn't suite the tanks atmosphere anyways...