Vanishing Blue Green Chromis

I have a 55G with Overflow and sump filter. I put in 3 Blue Green Chromis to start cycling finally. Last night i went to sleep, there were three like there were supposed to be, this morning i could only see two. I have checked everywhere and cant figure out where the third one went, down the overflow, in the fittings, in the sump, under the live rock caves, around the tank, i cant think of anythingelse.

If you have any ideas let me know, i cant even find remains.

I do have one small Emerald crab (yea maybe i shouldnt have him yet) to eat any remaining bubble algea from the Liverock, but still i would think to find a head or something even if it was him.

Thanks, Erik

Edit: And yes my tank tops fit very tight and they are 6" over the water height with only one spot like 1/4" wide that would allow a fish to exit the top of the tank without going over the top.

OK nevermind, my dad walked into the room looked in the fishtank and said hey is that a starfish overthere on that grey thing (powerhead), but it was just the tail of my chromis stuck to the inlet of the owerhead with the rest of him wrapped around the backside of the inlet, very very hard to notice as the tail of him was mostly transparent.

Guess that i just overlooked that spot, oh well, back to the fish store again

Erik