fish only question

Question
Thanks for reading my question.
I am a passionate but NEW Tank owner.
I have been running this 55 gallon saltwater fish only tank for 2 months. (live rock only)
All levels and tests come back great.
I had 6 Blue Green Chromis while cycling the tank
Only lost 1 Chromis in the Cycle (no body discovered)
Did my first water change... all levels looked good
bought 2 Percula Clowns...they were getting bullied by the 5 Chromis but they lasted a week
1 of the clowns disapeard in the night (no carcus)
I recently replaced the Percula with a percula TWICE as big.
He is doing fine.
But now the other smaller Percula disapeard last night (no carcus)
I've dropped the number of Chromis down to 3 and still have the bigger clown.

i am just nervous about ever adding more fish.
I have no clue where these clowns are disappearing to
thanks for the help
ps...nothing else was ever in the tank. last night i added 4 snails and 2 tiny hermits but i doubt that has anything to do with it.
i also checked the wet/dry floss and didn't find a body either.
it's a mystery! (but disheartening)
thanks for the help
jason

Answer
Hi Jason. Often when a small fish dies it can be very hard to find in a larger tank. With a good amount of rockwork in a tank the body can become lodged some where in the back of the tank and go completely unnoticed. If you have live rock in your tank chances are you have some kinds of scavengers in your tank that have hitch hiked in on the live rock. Creatures like bristleworms and small amphipods will often scavenge a carcass clean overnight. There is also the possibility of a small crab or shrimp coming into your tank from the live rock and it is not all that uncommon to get predatory crustaceans as well. Most of these animals can be very elusive only coming out during the period of darkness to either hunt or scavenge for food. Try waiting until your lights have been off for a few hours and shine a flashlight into your tank to see if you can catch them out. Snails and hermit crabs, even if they are small will also clean up the body of a dead fish rather quickly. One of the worst case scenarios that could happen in your tank is the introduction of a mantis shrimp brought in by your live rock. While not all that common it does happen from time to time. These shrimps will completely decimate a population of small fish and would have most likely eaten quite a few more than what you have lost so far. Chances are you have a simple but effective clean up crew from your live rock and that is where your fish have disappeared to. You may want to not add another fish for a week or so just to be sure that there isn't something lurking in your tank taking every opportunity to pounce on an unsuspecting sleeping fish. If more fish go missing in that time period you may want to set up some kind of trap to catch whatever it may be.