tank crash not mine though

A friend of mine runs a tank maintenence business. He set up I believe its either a 46 or 54 bow for a client. The tank was started in his house for I would guess 3 months using alot of rock from his 5 year plus old ytanks. I wanna say over a month ago the tank went to a dr.s office. At his house I know it had a pair of clowns a hippo tang and maybe 2 other fish and some corals maybe 40lbs of live rock. The tank went to the office added the rock water for the first day then maybe a fish or 2 and a few corals. It was doing well at his house I seen it myself. Not sure what fish stayed in the tank I know the hippo belonged to someone else so I know it didn't go. I think last week he went amd did the maintenance on it. Last sunday the owner who must be impatient added 3 fish. I think a hawk and a pair of cardinals. From what ive been told 6 hours later it crashed and crashed hard. He was there the next day and I think all fish dead 90% of corals dead. Frogspawn hammer completely melted even a kenya tree dead. My best guess was was the 3 fish caused it to re cycle. Kind of a small tank 3 fish is kind of a large load to add at once in a 50 gallon tank. Best guess tank has been up flr 3 to4 months. Mp10 reef breeders led. Thats most of what I know. I saw all his tests on a aquarium website the ammonia was .25 nitrates were at 40 but thats a day after the crash. Any thoughts on what can cause a good running tank to go in 6 hours. Im not sure if it would start a cycle in 6 hours thats were I think I may be wrong. I would think that would take atleast a day. No heater malfunction from what he says