I purchased a JBL bubble counter off the shelf at a shop a while ago (not my LFS) and when setting up my newest tank, was surprised to find that it did not seem to fit standard airline sized 4/6mm CO2 tubing. So its basically useless for me. Looking at the AquaEssentials page for this item http://www.aquaessentials.co.uk/index.php?main_page=product_info&cPath=196_308&products_id=629 (not where I purchased it... I found it on their site afterwards) it appears as if there is some non-standard tube size about "3-4.5mm". So basically my question is.... why? JBL sells 4/6mm tubing. What gives here? What other equipment is "3-4.5mm" equipped?