Rhinox Aluminum Alloy CO2 Bubble Counter - Aquarium Diffuser Regulator for Milwaukee Regulator Solenoid MA957 - CO2 Regulator for Aquarium - Tank Maintenance Tool - Carbon Dioxide Measurement Device ESSENTIAL HEALTH-TRACKING TOOL FOR AQUARIUMS  Takes the dangerous guess work out of wondering how much carbon dioxide is in your tanks water anytime. You literally just count how many bubbles! Although the Co2 bubble count varies for different tanks, but the rule of thumb is 10 bubbles per minute per 100 liter aquarium water. COMPATIBLE WITH MOST CO2 SET UPS  Although designed for the famous Milwaukee brand of aquarium accessories, Rhinoxs aluminum Alloy Bubble Counter works great with any diffuser and CO2 pump sets you might already have going on at home. CONVENIENT, WITH EASY INSTALLATION  Rhinox makes it easy for you to take care of your aquarium friends. This bubble counter comes with a built-in check valve and attaches to the regulator for an easy set-up. DURABLE  Made of sturdy quality aluminum alloy, this bubble counter is built tough to last and deliver. It is leak-proof to ensure no C02 escapes until you choose to unscrew it to refill with water. ECONOMICAL CHOICE  Cheaper when compared to more pricey solutions. The Rhinox Bubble Counter meets you halfway with a fair compromise between prices and build quality.