At those depths I bet my life on Poseidon Xstreams!

The Xstream second stage has a well proven construction with a number of newly developed characteristics. The inner volume, so called dead space, is small, which enables the build up of carbon dioxide to be minimized. At inhale and exhale the resistance is minimal, e.g. 0.07 Joule at inhale at 150 meters app. 495 feet depth. The exhalation diaphragm is protected by a cover that can be removed without using tools for easy access to the diaphragm. The diaphragm's position on the second stage also prevents flowing water from finding its way in to the valve.

The inner volume, so called dead space, is small, which enables the build up of carbon dioxide to be minimized.
At inhale and exhale the resistance is minimal.
The exhalation diaphragm is protected by a cover that can be removed without using tools for easy access to the diaphragm.
The diaphragm’s position on the second stage also prevents flowing water from finding its way into the valve.

Your mileage may vary!

Cornel