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Mystery of the disappearing fish...

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  • Mystery of the disappearing fish...

    In the last two months I've lost two fish under mysterious circumstances. The first was a juvenile yellow tang, 2" or so in size. A few days ago it was my bangai cardinal.

    In both cases:
    -it happened overnight. the fish was observed with normal behavior the day before.
    -there was absolutely no trace of the fish (skeletal remains or whatnot), checked filter socks in and around rocks, caves, sand bed, etc..
    -I immediately did a nitrate test when I noticed the fish missing and they were within normal parameters for me (10-20ppm).
    -Also did an ammonia test, all zero.
    -Also did a nitrite test, zeros.

    I have not introduced any new livestock into the tank in over 2 months, and the previous addition (mushroom rock) was quarantined for two weeks and dipped four times for safety (CoralRX, Bayer, ReVive, iodine).

    Suspect livestock:
    -Predatory mushroom - I have a largish elephant ear mushroom (4-6" across), and have read that these can be predatory and have seen the youtube video of one chowing down on a fish. However it's location would be a mystery as to how it got the cardinal, as they never came within two feet of eachother.
    -Christmas wrasse - 4", but I did not notice his stomach distended or anything the morning after, and also he's been peaceful with both fish since introduction (3+ months for the tang, 1.5 years with the cardinal). He has been known to take out snails though.

    So this leads me to believe that something like a mantis shrimp or bobbit worm snuck into my tank somehow. I've never heard the telltale "tapping" sound for a mantis shrimp, and have never stayed up into the early hours to check for worms of unusual size.

    Given the above, do you agree that I should be hunting for those hidden hitchhiker predators? Or is my cleanup crew good enough that all the hermit crabs and various other things cleaned up the evidence of a natural fish death in one night? The wrasse and my remaining clown pair all seem ok.

    Other things I had checked:
    -Confirmed heater was working normally as expected.
    -Confirmed no stray voltage (have titanium grounding rod)
    -Tested RODI water supply in ATO for same chemistry tests.
    -Nothing outside of normal in terms of scheduled water changes, cleanups, etc..
    75g corner acrylic pentagon DT with repurposed AIO chambers for marinepure reactor
    3x 50g acrylic frag tanks
    100g rubbermaid sump