Best Design, Construction and Performance AquaEuroUSA's Calcium Reactors are a simple and convenient way to maintain calcium and and alkaline levels in the tank. The Calcium Reactors include: Bubble Counter, Built-In Probe Holder, High Quality Pump and Multiple Unions for Easy Assembly. Superior Craftmanship High Grade Acrylic Construction High Quality Needlewheel Pumps Highly Efficient, Durable, Reliable Simple to Set Up and Operate