What do you mean by special nitro?? It's a commonly used breathing gas called Nitrox, which has some of the Nitrogen replaced by Oxygen, that's reducing the MOD (Maximum Operating Depth) because the PO2 (partial Oxygen Pressure) is increased. Nitrox is used for shallower dives, but with longer bottom time. Another gas used for deep diving is called Trimix where some of the Nitrogen and also Oxygen is replaced by Helium. Special training is required to dive on these gases. I don't know if this is the same guy but it's a french guy living on the South Coast guiding tourist divers on cave dives, this guy doesn't have the qualifications to do any cave diving whatsoever, he's also an "instructor" w/out instructor certification. His total diving experience is 2 1/2 years. I also know of a german guy, this one with a lifetime of diving experience, he used to be in the Sosua area. He was/is a proper cave EXPERT, don't know if he's around now. There is good diving in the DR. It's a lot better than it's reputation. Unfortunately most experienced divers go somewhere else. One of my best dives ever, anywhere in the world, was in Las Terrenas 3 years ago. We dove a small wreck off the coast of El Portillo 2 days after it sank (still got one of the maps). I can mention a few solid dive shops in DR I know (don't worry I don't get any comission). Casa Daniel in Bayahibe, North Coast Diving in Sosua, Treasure Divers in Boca Chica, Stellina Diving Center in Las Terrenas. All these are running a tidy business. Good diving.