| probably typing rubbish but was it possible that due to the hard physical effort at the beginning of the dive, you somehow "out-breathed / over-breathed" the unit [hyperventilation] and had a CO2 hit / build-up which got exacerbated with depth?
doubt if it was scrubber channeling as all was ok for the second dive.
my manual says 0-10 clicks. i know a couple of divers who dive their OPVs fully closed quite happily. it was trial and error for me re number of clicks until i was comfy. |