Actually, there are very nice places to scuba in Colombia. I am not a native to this country, so my information is only liimited to my personal experience.
1.- Cartagena de Indias
Incredible coastal city with a colonial air, worth seeing, declared international cultural city by UNESCO. A must see by everyone.
In front of Cartagena you have the Islas del Rosario which a group of small caribbean islands. According to alocal SCUBA shop there are about 40 different dive sites around the Islas del Rosario. I dived in a site called Caribarú which had an incredible coral wall - it was amazing (actually I am posting this right from the plane ride from this trip) and also a place called Punta Brava. Water temperature was at a balmy 28C.
2.- San Andres
A Colombian island which is closer to Nicaragua than Colombia, but it is Colombia soil. it is a rather large islands withi shops and such. There are also 5-star hotels (Sunrise is great) and has great snorkeling and SCUBA. You take a flight plane either from Bogota or Cartagena.
3.- Providencia y Santa Catalina
Providencia is a small island which you can actually go around completely in abuot 10 min car drive. You usually take a flight from San Andres to Providencia. Nice rural resorts, caribbean beaches, no shopping nor main plaza. Very good SCUBA too. Santa Catalina it its sister island which is even smaller and is connected to Providencia by a bridge.
Hope this helps you!
Regards,
Guillermo.:tree: