Corrected entry: During the climax, when Top turns on the air flow from his tank, he holds the pressure gauge in his hand so that the face of the gauge is pointing toward him. In fact, you are supposed to point the face of the gauge away from your body, so as not to cause injury if it the glass explodes. No experienced diver would make that mistake.
Corrected entry: Since a cave is a closed environment, you never use flares or any similar burning device inside a cave because it will fill it with smoke. That's a basic caving rule.
Correction: Lots of caves have ventilation through cracks in the earth, etc, and are not completely sealed environments.
Corrected entry: Throughout the movie the characters are talking to each other during their dives, yet they all have regulators in their mouths.
Correction: There are regulators available that allow speech between people wearing a headset. You still need to hold the regulator in your teeth, but it is airtight around the mouth, allowing you to speak into the radio mike that is implanted in the mouthpiece of the regulator. All those little red lights alongside the mouthpiece were the power lights for the radios and headsets.
Corrected entry: A biologist points out "white algae" in the cave. Algae need light to grow.
Correction: The parasites modified all the animals to be able to exist inside the cave, who's to say that they didn't modify the algae to do the same.
Corrected entry: When choosing a hole, one dude says "Smells like methane". Methane is odorless.
Correction: People make mistakes, and there are many dense people who say and do stupid things, hence this boils down to a character's mistake.
Correction: This is an "old wives" tale. Modern scuba pressure gauges will not experience a face explosion as there is a pressure relief valve in the assembly to prevent this exact thing from ever happening.