This aquarium fire occurred due to a poor connection at the pin on the light. Interestingly, we see an inordinately large number of aquarium fires due to ignition of the lights, heaters, and pumps. This can be due to poor connections, salt water corroding connections, salt water entering and short circuiting components, and other problems. Synergy Technologies analyzed this failure which led to a successful subrogation effort.
Shown below is the end of the light. The white dotted lines show the end of the fluorescent bulb and the red arrow shows the area burned away at one of the pin connections.