> From: nguyenh at nosc_mil (Hoa G. Nguyen) > > Where can I find a good back-flow-preventing valve for CO2 that won't > dissolve in the carbonic acid? And how much did you pay for it? We use Dupla "Bubble Counters" on our tanks. Besides acting as a bubble counter (an easy DIY project), they include a check valve. Pet Warehouse had them for around $35 the last time we bought one. George in Colorado with a "9" (5 degrees and 4" of snow).