Diving in Comoros is a bit of an unknown for most, and dive sites are untouched with very few visitors.
There is supposed to be a dive center somewhere on Grande Comore, but since I am unable to find any evidence of this, I will just mention the one that I know of, which is at Laka Lodge on the island of Moheli.
Here is a little extract from their website – go visit yourself – it is excellent.
“Mohéli Laka Lodge Diving is the only diving operation on the island and the first to explore and document the undiscovered waters of Mohéli. Since its creation in 2013, we have identified numerous attractive dive sites, while many others are still waiting to be discovered on the vast unexplored reefs of the Parc National de Mohéli which comprises a vast area of 400km² – 100,000 acres. We offer guided dives for certified divers and introductory dives (PADI Discover Scuba Diving) all year round.
PADI certification courses up to Divemaster level are offered during the high season between July and November. We organize two dives per day of which possibly one evening/night dive. Night dives are of an exceptional beauty.
To guarantee availability, dives and the rental of equipment need to be booked in advance.”