I got my open water scuba certification last year and thought I would be set for a while. When I started planning this trip and Belize popped into the picture, I began to check out getting my advance open water certification. The AOW cert is made up of 5 adventure dives; deep and navigation dives are required and then you get to pick 3 dives. In my opinion, the main perk of getting your advanced open water is being able to go to 100ft instead of 60ft. But you also get to try different things with an instructor present. I ended up picking peak performance buoyancy, fish identification, and night diving. That worked out to two dives per days plus a night dive. I had a chance to try out my new underwater housing for my canon S100 during 3 of my dives. I had done the test of holding it in the sink for 15 mins to see if there are any obvious leaks. There's a huge difference between 5 inches and 20, 60, 100ft of water. I was so so nervous the first time I took it to depth.
Peak buoyancy and navigation were up first. These were the most work intensive dives because I had to demonstrate control of fine tuning my buoyancy and navigate using three different techniques. After I completed my skills, we were able to dive around the shore off the dive shop. During one of these dives I some my first eel and a flounder and soon felt let I was in an aquarium tank. There were live coral heads around as well as sponges. That was also my first encounter with current. I don't know if I'm too streamlined or too much like a sail because the current could pick me and move me along easily.
That night I did my night dive. There's a general rule about night diving - Don't bring any new equipment. So of course I brought my camera and also had a torch to deal with for the first time. I was tempted by the lure of octopus, barracuda, eels moving about, and bio-luminescent plankton. After a few initial flailing moments in the darkness of the water, I settled into another world experience of only being able to see what was lite by my torch. Highlight of the dive was spotting three different octopuses.
The next day brought a deep dive to 100ft and my fish ID course. We took the boat through the rain to two different dive spots. The problem with being the least experienced diver is that I burned through air the quickest so I spent the most time bobbing in the boat which didn't do any favors for my stomach. Highlights from these dives included sea turtles, glimpsing a shark over the edge of the sea wall, and a pair of giant groupers. The current was very quick on both of these dives which required some pretty good buoyancy control and patience. My battery nearly died on the second dive of the day. I would have brought my second battery to change out but I was way too nervous about getting a tight seal and preventing the housing from fogging up to risk changing it. I understand why some people prefer video while scuba diving. The photography takes a really steady hand and dealing with a flash is much more difficult than I thought it would be. Granted my first night dive probably wasn't the best time to start messing with it.
My AOW course was a fantastic experience. My first day I worked with the head instructor and a newly certified instructor and the second day I was with the head instructor and while the dive master coordinated the rest of the people on the dive. Throughout all of the dives the professionals were pointing out interesting wildlife. The ridiculous rains the island was experiencing hurt visibility at many dive sites, but the dive master was able to recommend places that were not overcrowded and you could still see a good bit.
General tips: My recommendation for finding a dive shop on vacation is to go with one that will give you enough information that you feel comfortable up front in combination with good reviews on TripAdvisor and Scubaboard.com. I went with Blue Angels Dive Shop and Scuba School which is part of Blue Angels Dive Resort. They are a little ways off the main plazas on San Miguel but I think it's worth the walk or taxi fare. Everyone working there was polite and helpful. My advanced course included instruction, materials, gear rental, PADI fees, and a t-shirt for $365 including tax.
Disclaimer: Blue Angels did not request a favorable review nor did they give me any discounts. My opinions are my own.