Konaquatica Dive Center
Rebreathers and TecRec Trimix certifications are welcome when you come to Konaquatica. They're developing a reputation as the place for technical divers in Kona (although they take plenty of nontechnical divers to some of Kona's top dive sites). If there's anywhere in the world that the stealth and bottom-time advantage of a rebreather becomes obvious, it's Kona. The only thing better than seeing big animals is not sending them running with your bubbles.
Although I haven't dived it with a rebreather (yet!), I'd love to take one to the long-distance southern site called Au Au Crater. (One of the advantages of small, fast boats like Konaqatica's is that you can get to this site and still have plenty of time to really explore it without bumping elbows with other divers.) I'd like to explore this dramatic site sans bubbles so I can mingle more closely with the spotted eagle rays I've seen there; and the hammerheads that show up for me at Au Au always seem to be able to feel the pressure wave from my bubbles and head for the blue. I'd also like to get a chance to photograph, at close quarters, a Tinker's butterflyfish, a species that likes to hang in advanced-diver depths but is seen as shallow as 100 feet here.
Au Au Crater seems like an oceanic aquarium, harboring much of the wild variety of marine life found off Kona: dwarf eels, frogfish, piles of lobsters, snowflake morays, millet-seed, ornate and raccoon butterflyfish and, the patron saint of underwater Hawaii, the honu, or green sea turtle. The turtles in particular like to hang out on the lip of this massive underwater crater, almost as if they've stopped to check out the expansive view.
Although it requires a longer boat ride than most Kona sites, it's worth the extra effort to get there. And a nimble dive operation like Konaquatica is just the shop to make dives like this happen.