Welcome to the Board. I too would like to hear of particularly some shore dive sites in Columbia. I have not had much success googling the Pacific Coast there (Ecuador, etc.).
Well first of all it's ColOmbia, no "U". I can only speak of the Caribbean side but I hope to go to Malpelo and Gongora soon.
I got my certification in Taganga which is near Santa Marta. Average diving but very cheap. I'd stay away from Santa Marta where I've been once. Very polluted and especially El Rodadero, sewage water pouring into the sea there. A friend of mine who got me into diving told me a gross story about that place. She volunteered for a cleanup in Santa Marta and they split up into different groups. Her friend was assigned the Rodadero area and ended up covered in ****. Not at all interested in diving there again with the exception of going to the nearby Parque de Tayrona which is a sanctuary. If you're interested in Parque de Tayrona ensure that it's open; they normally close it for a month in January/February. BTW, Santa Marta is the only place I have ever dived in where I have seen debris, came across nets on each dive.
I used to not like San Andres too much until I switched to another dive center. The first dive center is co-located with one of the largest hotels and near the airport and downtown. I went out with those guys about 3-4 times and it was ok; about the same as Roatan. The last time I was in San Andres I decided to switch dive centers and chose one on the other end of the island. That was a much better experience and I would love to dive there again.
I've also dived Baru and Islas del Rosario off the coast of Cartagena. Hardly anything to see in Baru, the only reason I dive there is to compromise with my GF so that we can go somewhere where the only thing to do is not only diving. I though Islas del Rosario would be much better but no. Yes it's better than Baru but not a whole lot. I found it to be kind cloudy and the guide said it was because of recent storms but someone else told me that it's like that a lot because of silt coming from the Magdalena river. Another thing to note about to Cartagena; it's the most expensive diving in the Colombian Caribbean.
Providencia is a blast. Much better than Roatan. It's also very cheap. In Providencia you can get by speaking 100% English. The only downside is getting there. Satena which is actually run by the Colombian air force and a couple of other charter airlines fly there but you have to go thru San Andres - about a 15 min flight. You can also take a large
catamaran which depending on how rough the seas are can take 3-6 hours. When I took that trip I was the only one out of about 20 passengers to not get nauseous; it can get pretty crazy on that boat but very comfortable and they give you pills for sea sickness. When you go there you will see lots of sharks; go with a dive center that doesn't feed them. I did my AOW there and booked with an operator but switched to Sonnys when I learned that the former fed sharks. The sharks are getting more aggressive because of the irresponsible DCs and in fact a few weeks before I got there a diver was bit when she went out with the operator who fed the sharks.
Hit me up if you have any questions.