I used to live in ft myers, and worked on the ultimate getaway (which is the livaboard that does 3 day trips to the tortugas and back). The diving in ft myers is not great, but of course the tortugas are. There are a few decent spots though:
Captiva blue hole 25 miles- sits at about 70ft, the hole drops to about 160ft. Whale sharks seen here, sometimes big rays, and other neat stuff.
The Fantastico 30 miles- shipwreck in about 40ft of water (<- cant remember for sure on the depth). Big groupers, and big snappers. Bullsharks commonly seen here.
Hopper cars 23 miles- set of 5 or so train cars, very neat. Popular spearfishing location among locals, quite commonly visited by bullsharks.
Edison Reef 9 miles- Bridge rubble, not great, but close to shore (in comparison)
Thats about it. Theres a few other spots, but these are the good ones. Because of the location, Goliath Grouper are seen just about everywhere. Vis is usually between 15-35ft. 35 on good days.
Also, stop by the visitors center, they will give you a map with gps numbers for all of the locations listed.
P.S. I now live in key largo, if your coming to the area, msg me and Ill help you here. Maybe we can dive
