So, my experience with PL Divers (linked above) was mostly positive. They're attentive and international, which does not seem to be the norm across the MANY dive shops that have sprung up in town in the last five years. If you're going with a beginner, however, you're going to have to make a scene to make sure they don't take you to the outer waters, where you can get some rather low viz, heavy currents and washing-machine gullies, and coooold water. I told them my girlfriend had just finished her OW and they ignored that, which led to us cancelling her first dive and demanding our money back on it. Second through fourth dives in the inner waters went smoothly, including turtles and seahorses. All in all, Arraial is still a good spot to dive, but if you're forced to choose between there and some of the more famous spots in Brazil (Noronha, Abrolhos), just skip it and save the money. Hope that helps!