The Poseidon Xstream is Poseidon’s most recent regulator series and may be one of the answers for ice divers who are looking for a regulator that works well in extreme conditions. It is one of the few so-called “upstream regulators”, meaning the second stage needs to be pressurized in order to close. There is no piston that can become dislodged, misshaped or mis-aligned. Instead, a round stainless steel ball rests on the valve to always operate perfectly. The first stage is not environmentally sealed, but instead uses comparably huge openings to effectively allow water when diving in ice cold lakes, where the water temperature is around 3-6 degrees Celsius, to warm the metal parts of the XStream, preventing any form of ice build-up.