My clowns keep disappearing !

[Elvis1970]

I have had a 90 day reef tank running for over a year now going great except every time I try and add a couple clown fish they disappear within a week or two . Currently for live stock
I have a yellow tang , a blue tang 2 cleaner shrimp and corals . The picture shows the tank . I’ve checked the overflow and the sump as well . I just don’t get it I’ve lost 6 clowns in the past year

 

[Jake_the_reefer]

Wow that's weird. Only things I can think is they died and got eaten or if you have agressive species of anemones that are prone to kill clowns