Hi I wouldn't be concerned about your tank not being cycled after 4months of water in. Has your hand ever been in the water? Congratulations you've introduced bacteria for this process to begin... I don't understand why we're still trying to establish if the tank is cycled. He said no ammonia no nitrite. Yes there was an ammonia source... there's no need to ever buy a product to seed a cycle or let a raw shrimp decompose. Just un-needed. Like I've mentioned before, to cycle your tank add water and rock and wait. done done done. The idea that the bacteria colony would die is false.
Do you have a lid? Check behind the tank, did it jump? Pretty common for clown fish.
Other than that acclimation shock from salinity change. Or sick fish but probably one of first two.