Ok...thanks for the suggestions. My air filter does not have any arrow (supposed to be on the outer ring white part of the disk?). Checked it 3 times. Its been kept dry.
The pump does build up pressure in the tubing when I hold my finger over the end, but does not seem very powerful. It doesn't exactly "whisper" either.
I'm going to pick up a larger pump from the pet shop and try the stone with no filter, for testing purposes. If that works I'll try the filter and aerate my wort (after sterilization). If it doesn't I'll know its the stone.

BN Army

