Many divers I met recommended taking the course and getting certified in Nitrox diving. Nitrox is the commonly used term for enriched air, or air that has more oxygen added so it's above 21%, and thus less nitrogen. For recreational divers, we could dive with enriched air with up to 40% oxygen. The course was just me again, and the instructor was the same one from my Advanced Open Water, N. The course consisted of watching yet again another DVD, some lectures, a multiple-choice exam, and two dives using Nitrox. N was also a certified Nitrox technician, so he also had me help him do the air mixing, and the air we mixed would be used during our dives. N taught less "by the book" and more by experiences, so I found the nerdy stuff he shared on gas mixing, oxygen toxicity, and decompression illness very interesting.
We mixed four tanks of EAN32 for our dives, i.e. Nitrox with 32% oxygen. The process he used was to blend 100% oxygen with air in a tube first, and the mixture is then compressed and put into regular air tanks. He explained making Nitrox was both an art and science; he would adjust the pure oxygen input by +/- 0.5% to take into account burn rate and other factors in order to produce the desired % of oxygen. Since the % of oxygen has a direct impact on dive planning (i.e. more oxygen means you can dive longer, but on the flip side there's the risk of oxygen toxicity), the amount of oxygen must be within 1% of the stated %, so if it's EAN32, then the actual oxygen % may be between 31.1 to 32.9. Our four tanks of EAN32 were all within 0.5%.
For our two dives, we dived at Chumphon Pinnacle and No Name Pinnacle. N was very knowledgeable about fish and other marine life, so coupled with the extra amount of time we could dive, I had two amazing dives and saw and learned loads of new marine species. At Chumphon we went to the maximum 30 meters and dived for 47 minutes; visibility was very good thus allowing us to see more. There were giant groupers (by giant, I mean almost 1 meter long), scorpion fish (so hard to spot with their great camouflage), and the fabulous banded boxer shrimps. At No Name, we went to 27 meters deep for 50 minutes, and saw so many species, I could not remember all of them afterwards! There were at least five blue-spotted sting rays, puffer fish, and long-fin banner fish, the latter two were both in Finding Nemo. N somehow managed to find these juvenile pipefish that were super tiny (thinner than the pinky) and hung out on tall seaweed; he was very, very excited, said it was only the second time he has ever found them, lucky me! There were all kinds of shrimps: durbin dancing, glass, bubble anime, and sword blade. We also saw huge schools of chevron barracudas and tiger cowrie shells where shrimps made their home. The amount of "life" happening around me was unbelievable! I wished I could have spent another hour underwater, but even EAN40 would not have made that possible.
Once we finished the dives, I took and passed the multiple-choice exam, fourth course done and another certification!
The two dives didn't feel any different to my body from regular dives; in talking to other divers, they said the difference would have been more obvious had I dived with Nitrox consistently, because it should be gentler on the body given the higher % of oxygen. Who knew even air could be so complicated and interesting at the same time!
