"Tastes like a septic tank, smells like your old man's farts and gives you a horrid case of diarrea. Use it too much and you'll grow hair on your tongue." Fortunately these were NOT the first words out of the mouth of my instructor, as I studied to get my nitrox permit for scuba diving. He did however, warn about the possibility of oxygen toxicity, as breathing too much of the stuff isn't good for your brain or lungs.
I suppose I should start with a better explanation for all non-divers reading this. When you dive, your body absorbs nitrogen in your bloodstream. If you absorb too much, either by diving too deep or diving too long, the nitrogen builds up, and causes all sorts of serious health problems (which explains Michael Jackson and TomKat). So divers carefully measure, monitor, and limit the amount they absorb. Unfortunately, this limits the number of dives you can do and your options when diving.
SO, how do divers get around this? Since nitrogen is the problem, why not just breathe a mixture of gas with less of the stuff in it? Enter enriched air nitrox (to thunderous applause). Normal air consists of 21 percent oxygen and 79 percent nitrogen (except when my dad uses small lavatories). But Nitrox contains 32% or 36% oxygen. So you breathe more oxygen and less nitrogen at depth and your body absorbs less nitrogen, so you might be able to do that fourth dive without having to worry about pressure sickness.
The downside? Increased risk of oxygen toxicity. You can have too much of a good thing. Equipment also oxidizes faster and there's an increased risk of fire/explosions (just like my old man's farts).
But all in all, if you are doing lots of fairly routine dives over multiple days, nitrox might be the way to go, despite all the hassles associated with it.
As for Sharm El Sheikh and the Red Sea, the diving is fantastic, but it doesn't quite live up to the legend that divers had put in my mind. The famous wreck in the area, the Thistlegorm, was allegedly closed, and a little piece of my heart died inside. The reefs were in decent shape and the visibility very good. 20-25 meters at best. But the Red Sea is famous for 30-35 meter visibility, and this just didn't happen. The coral reefs were quite pretty, but overused. Every dive site we went to had 3-7 other boats, glass bottomed boats, and snorkelers. You couldn't dive anywhere without the sound of motors or engines somewhere in the distance.
Nevertheless, with as much traffic as I saw, the Egyptians seem to be doing a decent job preserving the reefs. One thing didn't surprise me though. I was underwater, and another diver pointed out a huge eel that was probably 5 feet long and weighed 40 kg or more. Impressive. He pointed to a nearby reef shark after that. Then he scribbled, "TIPS 3$", on his clipboard.