Aquarium Murder mystery

Alright now another piece of the puzzle, I found my watchman goby completely attacking my coral beauty today TWICE! Although I read they’re peaceful and can’t find a ton of examples of people with aggressive YW gobies.
 
urban legend lol GIF by Animation Domination High-Def
 
Slightly low salinity for inverts. Very high temp IMO. But i doubt those are the culprit. Nitrate is reasonable/no-issue.

I can rule out most of your livestock as the culprit as they werent there since the beginning, and you are having repeated symptoms/indicators since day 0. ...unless there is a copycat killer of a previous now-dead killer. Lol

Joking aside: what species of hermit? Upload a photo of his face/claws if you dont know. Different hermits have generally different temperaments.

My primary guess is disease, parasites, or... you missed another option... a pest. There are non-disease non-parasitic pests that are predatory and reclusive. Examples include various worm species such as the dreaded bobbit worm. You could have something hiding in the shadows.
Didn't know bout temp and salinity, I'm gonna try to lower those, thx!

your right about most of livestock being not eligible for the killer, so the main suspects would be

Clownfish: cute, tiny, might have killed his mates in the past, schools with chromis

YW Goby: territorial, grumpy, a get-off-my-lawn sort, not the kill-you-behind-my-shed-with-a-meat-hook sort, but has been known to attack my coral beauty, and chase the lawnmower blenny(which is dead now).

Pistol Shrimp: Again grumpy and territorial, only attacks things that go right in front of the burrow, and really he just snaps a little at them.

Big ole hermit: doddering, kinda keeps to himself, saw him once attack my Foxface, but otherwise, no aggression always found eating the dead fish

Emerald Crab: no aggression i've seen, eats algae, is nocturnal, no signs of aggression

Velvet: possibility to me not knowing good qt procedure. But find it odd that only it only affects bottom-dwelling fish and Hawkfish and Blennies are far more resistant to disease than say fox faces and Angels, I did see fast respiration on hawks but that could be a myriad of reasons. And I've never ever seen gold dots, and I've looked really close.

Bad water quality: possibly, I just found out the tests I'm using (API test kit) are not that accurate so could be that.

live rock pests: possibly, but I've never seen any and I tend to watch my tank pretty close. plus I would imagine a Bobbit would swallow a fish not hurt them, But kinda want it to be bobbit cuz I grew up watching them on documentaries and would be sweet to see one in the flesh, on the same note anyone been seen or hurt by bobbit? Gorrilla Crabs freak me out. And could bristleworms do anything?

Magic aquarium elves who want to torture me by killing fish: low probability but I wanna cover my bases.
 
I'd put a decent size shrimp in the corner away from the rock work on fishing string or a skewer... Maybe you have an aggressive emerald crab or Gorilla crab. do it at night and check it every 30 minutes or so... I had an emerald crab that would get my lower level fish... And eat em..

Or it is your original clown... Unless I missed that he/she passed too
Hold on, you had Emerald that killed things! People told me that it was a "0% chance" of him attacking or eating any fish. This hobby can be so confusing sometimes.
 
Didn't know bout temp and salinity, I'm gonna try to lower those, thx!

your right about most of livestock being not eligible for the killer, so the main suspects would be

Clownfish: cute, tiny, might have killed his mates in the past, schools with chromis

YW Goby: territorial, grumpy, a get-off-my-lawn sort, not the kill-you-behind-my-shed-with-a-meat-hook sort, but has been known to attack my coral beauty, and chase the lawnmower blenny(which is dead now).

Pistol Shrimp: Again grumpy and territorial, only attacks things that go right in front of the burrow, and really he just snaps a little at them.

Big ole hermit: doddering, kinda keeps to himself, saw him once attack my Foxface, but otherwise, no aggression always found eating the dead fish

Emerald Crab: no aggression i've seen, eats algae, is nocturnal, no signs of aggression

Velvet: possibility to me not knowing good qt procedure. But find it odd that only it only affects bottom-dwelling fish and Hawkfish and Blennies are far more resistant to disease than say fox faces and Angels, I did see fast respiration on hawks but that could be a myriad of reasons. And I've never ever seen gold dots, and I've looked really close.

Bad water quality: possibly, I just found out the tests I'm using (API test kit) are not that accurate so could be that.

live rock pests: possibly, but I've never seen any and I tend to watch my tank pretty close. plus I would imagine a Bobbit would swallow a fish not hurt them, But kinda want it to be bobbit cuz I grew up watching them on documentaries and would be sweet to see one in the flesh, on the same note anyone been seen or hurt by bobbit? Gorrilla Crabs freak me out. And could bristleworms do anything?

Magic aquarium elves who want to torture me by killing fish: low probability but I wanna cover my bases.
Bobbits wont swallow fish like that. You may be recalling them dragging fish into the sand. But if they live in a rock (as one did in one of my previous tanks), they will just take bites.
 
just about any crab will grab just about anything withing claws reach.

I don't think you have an unknown predator (like a Bobbitt worm) cause you keep finding the dead fish.

To be honest though - with all the additions you've been doing - it's very possible you have a disease or parasite running through the tank.

Watch who is eating and how much very carefully - and watch for weird breathing, cloudy eyes, weird looking fins, skinny but eating (this is a big one IMO - and easy to treat).

I also am not sure about you having measurable nitrites - unless you have a huge bioload or a large spike, I don't believe you should ever be able to measure nitrites in a SW tank.

Are there known parasites that kill within 2 days, I assumed that it was a long period of time. plus the waste on most fish look good, and I thought parasites would cause death over a good period of time, and the quick deaths would be something like velvet.
I had a bacterial bloom at the time, and I checked water read 0 ammonia and a crazy amount of nitrite. might have been a fault on the testing kits end but it, but I did check it 3 times cause I thought it was weird as well
 
Bobbits wont swallow fish like that. You may be recalling them dragging fish into the sand. But if they live in a rock (as one did in one of my previous tanks), they will just take bites.
Again someone told me they would only eat fish whole.... smh.
 
@ActiveAngel do you have any pics of it? would really like to show my brother. thx!
No good pics. It was a long time ago, always hid in the tiny tunnels of a large rock. It took 3 years before i realized it was even in the tank. Black in color, lightning fast, nocturnal. I only noticed it because one of my massive hermits (3-4") was always harassing him.

Basically the hermit would go to his rock, and pick at the rock. I thought he was just grazing. Little did i know that this would draw out the bobbit, which would try to attack the hermit. And the hermit would attack back.

Speaking of; maybe i missed your response. What type of hermit do you have?
 
Hold on, you had Emerald that killed things! People told me that it was a "0% chance" of him attacking or eating any fish. This hobby can be so confusing sometimes.
I feel Like i did. Yes.

For a short while they're starting to lose fish that slept in the rocks or sand. Three pipe fish. Six line wrasse, 2 gobies.

Soon as I remove the emerald crab I have never had lost another fish, even after adding more.
 
No good pics. It was a long time ago, always hid in the tiny tunnels of a large rock. It took 3 years before i realized it was even in the tank. Black in color, lightning fast, nocturnal. I only noticed it because one of my massive hermits (3-4") was always harassing him.

Basically the hermit would go to his rock, and pick at the rock. I thought he was just grazing. Little did i know that this would draw out the bobbit, which would try to attack the hermit. And the hermit would attack back.

Speaking of; maybe i missed your response. What type of hermit do you have?
sorry was out at the time had to wait to get a pic of him.
here he is:
 

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I feel Like i did. Yes.

For a short while they're starting to lose fish that slept in the rocks or sand. Three pipe fish. Six line wrasse, 2 gobies.

Soon as I remove the emerald crab I have never had lost another fish, even after adding more.
Same thing happened to me with fish. were they just dead or were they eaten?
 
No good pics. It was a long time ago, always hid in the tiny tunnels of a large rock. It took 3 years before i realized it was even in the tank. Black in color, lightning fast, nocturnal. I only noticed it because one of my massive hermits (3-4") was always harassing him.

Basically the hermit would go to his rock, and pick at the rock. I thought he was just grazing. Little did i know that this would draw out the bobbit, which would try to attack the hermit. And the hermit would attack back.

Speaking of; maybe i missed your response. What type of hermit do you have?

Bobbits are truly the stuff of nightmares I swear, how did you remove it?
 
That is a Thinstripe Hermit Crab. Not common, but not rare. Not reef safe. Moderately aggressive. They get pretty big, much larger than yours, but not huge. And is one of the few types of hermits i dont trust in anything but a predator tank. I continue to suspect he is your culprit.

Removing the bobbit, from a large central base rock, was a long and arduous process, taking 6-10 months. I could write 20+ paragraphs on all the various attempts and partial successes. In the end, it required removing the entire rock and chemically killing it (bleach, rinse, dry, acid, rinse, dry, then back to the tank).
 
Are you sure it's not a hitchhiker that came in as a baby and then grew large enough to prey on your fish? Mantis shrimp are notorious for it but they'd be knocking off the inverts first I'd think. I once discovered an 8 ft long eunicid worm living in a 40 lb piece of LR. It'd burrowed all inside of it. I only noticed bc the zoas on the rock stopped opening and I notice a very small head of something poking out when feeding my fish. You can turn off all the lights at night and get it pitch black and use a red light to search for creepy crawlies that only come out in the dark bc they can't see the red light. Another fun fact is those big worm monsters hate carbonated drinks. After breaking my rock in half I dumped sprite on mine to get it the rest of the way from the rock and into a bucket. I was gonna keep it and name it big worm after the guy from Friday but the gf said no way.
 
Are you sure it's not a hitchhiker that came in as a baby and then grew large enough to prey on your fish? Mantis shrimp are notorious for it but they'd be knocking off the inverts first I'd think. I once discovered an 8 ft long eunicid worm living in a 40 lb piece of LR. It'd burrowed all inside of it. I only noticed bc the zoas on the rock stopped opening and I notice a very small head of something poking out when feeding my fish. You can turn off all the lights at night and get it pitch black and use a red light to search for creepy crawlies that only come out in the dark bc they can't see the red light. Another fun fact is those big worm monsters hate carbonated drinks. After breaking my rock in half I dumped sprite on mine to get it the rest of the way from the rock and into a bucket. I was gonna keep it and name it big worm after the guy from Friday but the gf said no way.
No, the weird thing is my inverts do great. I've only lost one and I have tons of them, fish do poorly. so I don't think that's it. good idea tho.

8 feet!!!!!!!! Dude, I would have burned that thing. but the idea of you pouring sprite into a bucket and yelling "Die foul fiend" on your front lawn fills me with happiness 😂. Do you have any pics of that creature?
 
@Olong317700 Yup, similar experience. Hiding inside a large live rock. Mine was also munching on zoas... in a preferential order. It wouldnt attack one colony until the prior one was completely gone. Red light didnt scare mine as readily either.
 
@Olong317700 Yup, similar experience. Hiding inside a large live rock. Mine was also munching on zoas... in a preferential order. It wouldnt attack one colony until the prior one was completely gone. Red light didnt scare mine as readily either.
It wasn't a fun experience. All I saw on its head were tentacles, no snapping jaws like a Bobbitt worm. It must've had some powerful mouth parts to burrow all through that piece of rock though. It was easily over 60 lbs, that's with it hollowed out apparently. I never saw it come out of the rock until I forced it. I think I was spot feeding marine snow and I saw it's head poke out of the hole ever so slightly, right where I noticed my zoas were doing bad. That rock was covered in zoas and that was the only spot doing poorly. I knew whatever it was I wouldn't be able to get out in a reasonable manner. I thought of covering it's hole with kalkwasser like some do to aptasia, but that'd be an eyesore to me. So I went scorched earth and split the rock down the middle. There are lots of types of these worms apparently and not a lot is known about them, especially in the ocean. One that is 50 ft long is the stuff of nightmares but we have no way to know how long some grow in the wild, they're so secretive and shy. Some marine biologist simply spectate that some species may grow that long. At least we know their kryptonite: sprite.

It was probably less than an inch long when it hitched into the tank, it'd been a very long time since I added LR. It was suggested mine was from Fiji and indeed, much of my rock came from there. At least mine wasn't thicc like some vids I've seen online, and it had the good manners to stay out of sight. I saw a video of one that looked almost as big around as a water bottle just patrolling the substrate in broad daylight. It set off a primal revulsion deep in the oldest, most primitive part of my brain.

I won't hear an ill word said of mantis shrimp though. Yes they can be murderous hitch hikers just like aileen wuornos but they're one of my very favorite things I've kept in a species tank. They're a joy to keep as long as you keep them alone.
 
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