Fish just dissappear sometimes Jiddy. Unfortunately that's a part of this hobby sad as it is. Corals bleach, fish die, cualerpa goes asexual, skimmers plug up, heaters stick, chillers go out etc. etc. etc. You can't give up man, buy something cheap and inexpensive like the chromis and see how they fare. We were emptying my friend's 75g because it sprung a leak and found a purple pseudo in the overflow that had been missing for three weeks. It was hiding in the corner and the only reason we found it is because it started flopping around when the water got low! My Engineer Goby went AWOL for 5 weeks until I found under the pump in the sump alive and well and about an inch longer than when he dissappeared!