I never found, as the medical officer, any severe mental problems. Interestingly for such close quarters there weren't any fights. By providing excellent ( for the military) food and flexibility in eating helped considerably. We had at least one movie per day. Our tour was 56 days submerged. The worst problem was the lack of out going communication--none and only three 17 word cables from home per patrol.
CO2 buid up was eliminated by CO2 scrubbers and I have no idea how they worked. Oxygen was produced on board by O2 generators using the hydrolysis of water. That is the beauty of a nuclear power plant.
As far as sea life the worst problem was when the fish died in the aquarium in the wardroom. Remember your encased in a hardened steel tube that can stand at least 700 foot of depth and the submarine weighed in at 8,000 tons and 450 feet long.
Were you ever deployed to a submarine that did not use nuclear plants?
What kind of fish were in the aquarium and how were they dying?
Did you ever meet Admiral Rickover?