5 fish dead over the last week, but my fire shrimp, pistol shrimp, hermit crabs, snails, and coral are all still alive and well. What is going on???

greenbean04

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So I’ve had this 35 gallon saltwater tank for over 2.5 years and I’ve had major issues of aggression between my fish, especially when I had my pair of clownfish who I ended up rehoming. In the past few months I got a Midas blenny, 6 Blue-green chromis, a fire shrimp, and I’ve had a watchman goby for the past 2 years who bonded with a pistol shrimp 1 year ago. I feed three times a day and sometimes even more by spot feeding some frozen food. The Chromis fish were slowly picked off until I had 2 left as of last week. I went on vacation and both of the fish were gone and my watchman goby was no where to be found. I woke up this morning to my electric blue hermit eating the dead Midas blenny. So now I have no fish in my tank and I’ve never experienced anything like this since being in the hobby for over 5 years now. I have lots of different hermits, different snails, bristle worms, spaghetti worms, and as of recent I found 2-3 rather suspicious “bristle worms” in the back of my tank (it has the body of a bristle worm but its hairs are 3 times as long and go from red at the base to white tips *see the attached picture*). I have lots of hiding spots for fish and plenty of rock/ coral to swim through and around. I’ve tested my water parameters and everything is within normal ranges. What could be happening?? Are the scavengers of the tank attacking my fish at night? Are my shrimp killing my fish? Any ideas as to what might be going on and what I should do next? I got into this hobby for the fish and I can’t see myself having a salt water aquarium without fish. I feel like I’ve tried a variety of fish but somehow one of my “peaceful” fish end up becoming aggressive and bullies all the other fish.
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What I would do:
Potassium chloride 1tbls/gallon.

1St remove “good” invertebrates and put them in a holding tank with air.

Add KSP with circulation pumps working.

After an hour drain all water and dispose of it. Remove dead inverts with the old water. Used a gallon or two of clean water to rinse the sand, or just remove the sand and rinse it thoroughly in a bucket before adding back into the tank.
Refill the tank with new saltwater.
Put the good stuff back and add new fish in a week.

New Years Champagne GIF by UKTV Australia
 

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Is everything just disappearing and you don't find remains? What condition are the dead fish in when you find them?

This sounds like a disease plagued tank to me. With high fish aggression, like you stated, disease would have an easier time taking over.
What are your water parameters as well?
 
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greenbean04

greenbean04

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Is everything just disappearing and you don't find remains? What condition are the dead fish in when you find them?

This sounds like a disease plagued tank to me. With high fish aggression, like you stated, disease would have an easier time taking over.
What are your water parameters as well?
because I have 10-15 hermit, 10-12 snails, 1 fire shrimp, 1 pistol shrimp, and bristle worms throughout the tank they all eat anything dead before I am usually able to find it. Today was the fish day in over 6 months I was able to see a dead fish (the Midas Blenny) being eaten. Also the fish were doing well for over 4 months until as of recent (1-2 weeks). The only new addition to the tank was a Duncan coral (added 3 weeks ago) and no new coral, fish, or invertebrates have been added in months.

Parameters:
Temperature: 79 degrees Fahrenheit (I might turn down to 77-78 if that is recommended)

Salinity: 1.025 SG
pH: 8.2
Nitrite: 0 ppm
Nitrate: 0 ppm
Phosphate: 0 ppm
Ammonia: 0 ppm

I haven’t tested Calcium, Alkalinity, or Magnesium today, but once I do I’ll post the results here.

My water is very clear, there is minimal to no algae growth, the sand is clean looking, I’ve never had any sort of crash in my tank, when observing my fish before leaving from my week long trip my fish showed no signs of being diseased. However, one out of the three Chromis fish that passed 2 weeks ago had a massive chunk of its tail bitten and was very skittish. Additionally, when I found that fish in the verge of death it looked like something snatched the fish by the mouth or the fish got stuck somewhere by its mouth because it was basically detached and one of its side fins had been bitten off. Lastly, it was swimming frantically and sidewise before I was able to catch and euthanize it.
 

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That is what I was thinking. 35 gallons is too small for such large and aggressive fish.

For perspective, I have a 50 gallon with 20 sump and I have 2 clownfish, a royal gramma, a yellow watchman goby, and a neon goby. I've had this stock for 7 months but I am adding a carpenters wrasse, 3 yellow striped cardinalfish, and a tailspot blenny very soon. All of my fish average out a max size of 3 inches and are known to be peaceful.
 
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That is what I was thinking. 35 gallons is too small for such large and aggressive fish.

For perspective, I have a 50 gallon with 20 sump and I have 2 clownfish, a royal gramma, a yellow watchman goby, and a neon goby. I have had this stock for 7 months but I am adding a carpenters wrasse, 3 yellow striped cardinalfish, and a tailspot blenny very soon. All of my fish average out a max size of 3 inches and are known to be peaceful.
I used to only have a clown fish and a watchman goby and both of the fish were incredibly aggressive towards each other and any new additions. After rehoming the clown fish is when I got the 6 blue-green Chromis, which was recommended by my LFS and they did really great with the watchman goby, but as soon as I added the Midas blenny, which I thought were fairly peaceful, that is when things went downhill. So should I maybe just do a pair of clownfish and maybe another watchman goby and call that it as far as fish in the tank? Or do you have a better recommendation on what type of fish/ how many?
 

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I used to only have a clown fish and a watchman goby and both of the fish were incredibly aggressive towards each other and any new additions. After rehoming the clown fish is when I got the 6 blue-green Chromis, which was recommended by my LFS and they did really great with the watchman goby, but as soon as I added the Midas blenny, which I thought were fairly peaceful, that is when things went downhill. So should I maybe just do a pair of clownfish and maybe another watchman goby and call that it as far as fish in the tank? Or do you have a better recommendation on what type of fish/ how many?
I would add more rock to the aquarium first. That will give the fish more to explore and distract them. It will also give them more hiding places when someone is being mean.

Then yes, you could do 2 clowns and a YWG. I would try to get snowflake clownfish or another Ocellaris species. That is important because some clownfish are more aggressive. I have snowflakes and mine have been amazingly peaceful is why I recommend them.

If the rockwork is good enough you could probably add another fish. Any of the fish on my list would work great except the carpenters wrasse. Maybe a possum wrasse if you have some good caves/hiding spots. They are very reclusive fish but I love their personality in fish stores.
 
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I would add more rock to the aquarium first. That will give the fish more to explore and distract them. It will also give them more hiding places when someone is being mean.

Then yes, you could do 2 clowns and a YWG. I would try to get snowflake clownfish or another Ocellaris species. That is important because some clownfish are more aggressive. I have snowflakes and mine have been amazingly peaceful is why I recommend them.

If the rockwork is good enough you could probably add another fish. Any of the fish on my list would work great except the carpenters wrasse. Maybe a possum wrasse if you have some good caves/hiding spots. They are very reclusive fish but I love their personality in fish stores.
Awesome! I really appreciate the advice and recommendations!!
 
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greenbean04

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To be honest you have a lot of aggressive fish in a smallish tank and no hiding spots, just the arch. I would suggest to add more rockwork (nooks and crannies and tight little caves) or select more peaceful fish. Good luck
Will do thank you for the recommendation!!
 
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greenbean04

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I hear it so much but mine are so great!
They are my oldest fish and I'm still waiting on them to turn to the dark side lol.

20241006_220012(0).jpg
I’ve never had snowflake clowns so I think I’ll try to go that route and hope for the best. Also I see you have an urchin, do you like having it in the tank?
 

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I’ve never had snowflake clowns so I think I’ll try to go that route and hope for the best. Also I see you have an urchin, do you like having it in the tank?
Oh yeah! He seems to clean up the place nicely but he does move things a lot.. I have a pistol shrimp as well so I have to tie everything down anyway.
 

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Midas blenny, 6 Blue-green chromis, a watchman goby


ALL dead? As in NO survivors?

I am sure there was aggression as midas blennys hate small tanks and chromis tend to pick on each other but...

if every single fish is wiped out and you QT nothing, probably also disease.

I would do 45 days at 81 degrees NO fish to '"fallow" before trying more to be safe.
 
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greenbean04

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Midas blenny, 6 Blue-green chromis, a watchman goby


ALL dead? As in NO survivors?

I am sure there was aggression as midas blennys hate small tanks and chromis tend to pick on each other but...

if every single fish is wiped out and you QT nothing, probably also disease.
So the 6 Chromis fish didn’t die all at once. 4 of them passed over time from the blenny picking in them and the Chromis also bullying each other. So in total 3 fish died over a week and 1 fish died the next week. I caught the blenny picking on all the other fish very frequently and the watchman goby was a couple years old.
 

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