Diving in Cartagena
Because diving is pretty indescribable, and if you're still in Colombia why do not you look into their coral. And yes diving in Colombia can be as safe as in your own country.
Rent only material with dive clubs where a lot is rented.
Rent not any old or very new materials (both you have to think why would anyone else use it)
DAN and PADI dive approve their hiring. On their website you can see who is connected with them.
Several reputable organizations:
By Padi 5 star rated diving school. Diving almost always will find place in the Rosario Islands or is possible off the coast in Cartagena.
Dolphin Dive School
By Padi 5 star rated diving school. Has its headquarters on the Rosario island Pavito, but has an office in the old town.