Hey DougieG
Divers Paradise is right on Key Biscayne. We've done some wrecks with them and they also help the local U of Miami with volunteer dives for their Rescue a Reef program. They did cancel on me a couple of times though but when we did go out it was a good experience. Their calendar looks pretty full :
DIVE AND SNORKEL TRIPS | divers-paradise (keydivers.com)
There is also Tarpoon Lagoon Dive Center (
Tarpoon Lagoon Dive Center | Miami Beach | Scuba Diving | Snorkeling) and Deco Divers (
Scuba Diving Miami | Snorkeling | Rentals | Deco Divers - (decodiversmiami.com) that go out of South Miami both of whom we have used and had a good experience. We've done reefs and a few wrecks with them. Also the Neptune Memorial Dive site out there which was pretty cool.
Neptune Memorial Reef
There is also a cool site called 'Army Tanks' which you might be able to request.
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The Teneco Towers is an amazing site too, you'll have to be further north for that one. You might try
ScubaFortLauderdale.com - Home of the American Dream II for that one. We have used them often and they are great. No shop (so no rental gear as far as I know), you'd have to arrange that elsewhere.
Lots of small wrecks in the area and a some great spots on the reef. A few other articles from my wife's blog (some are further afield) for your reading pleasure:
South Florida Diving Archives | Freedom Tour Travel
Enjoy your stay, and hope you get to go diving