Nothing in Belize that I know of as far as a Pool you may be getting mixed up with the pool in Puerto Rico called Bioluminecent Bay
Located in Puerto Rico, on Vieques Island, there is a shallow body of water with a narrow inlet known as Mosquito Bay. In each gallon of the bay there are 720,000 phosphorescent single-celled organisms that glow when they are agitated. It is a defense mechanism — the glowing is designed to daze whatever predator is bothering the tiny dinoflagellates.
All together the bay, on a moonless night, will produce more than enough light to read. Swimming in Mosquito Bay will cause your limbs to be bathed in blue-green light. If you stop moving the light will dim, and eventually disappear completely, but each time you twitch it begins anew.