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???

[Tamberav]

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.

watchman goby live longer than a couple years (expect 10+) and what killed your last fish?

Disease.

Lets face it... 7 fish added with no QT... there was aggression yes, there was also most likely disease as well.

 

[KrisReef]

Rats
In overcrowded cages exhibit much greater aggression than rats that have plenty of cage space. They eat each other before any sickness occurs.

 

[greenbean04]

Rats
In overcrowded cages exhibit much greater aggression than rats that have plenty of cage space. They eat each other before any sickness occurs.

By the time there were a total of 5 fish do you think that the aggression was already in place so that’s why it continued to the end?

 

[Schulks]

By the time there were a total of 5 fish do you think that the aggression was already in place so that’s why it continued to the end?

There was certainly disease too. It is hard to hear but you should do a long fallow period before adding more fish. It would help a lot.

 

[unclejed]

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.

My first guess is that it is the Pistol Shrimp. This has been discussed here. The Clowns are fine. Fish are like people, some good, some bad, if they have been ok so far chances are they will stay that way. If they host an Anemone all the better.

 

[TaylorLee]

I would test for stray voltage in the tank. If you don’t have a grounding probe in the main display and sump tanks then I would do that immediately

 

[BryanM]

I tend to agree with too many fish in a small tank, and 100% not enough rockscape for hiding places.

I also am suspect of 0 nitrate and phosphate, but that's not the issue. Both of those numbers at 0 is not good though.

 

[greenbean04]

There was certainly disease too. It is hard to hear but you should do a long fallow period before adding more fish. It would help a lot.

Someone else mentioned I should turn the heater to 81 degrees Fahrenheit, do y oh agree? Or should I keep the temp @79?

 

[unclejed]

Someone else mentioned I should turn the heater to 81 degrees Fahrenheit, do y oh agree? Or should I keep the temp @79?

79 to 81 isn't much of jump. I have mt water temp at 82.5.

 

[greenbean04]

79 to 81 isn't much of jump. I have mt water temp at 82.5.

Okay good to know

 

[Schulks]

Someone else mentioned I should turn the heater to 81 degrees Fahrenheit, do y oh agree? Or should I keep the temp @79?

Raising the temperature is a good idea. It can help speed up the clock on disease so I agree.

If you are going to do a fallow period you could use the time for some quarantine on your new fish.
You would just need another setup and some cycled media for the filter. I've always used seachem tidal HoB filters. If you are in any reef groups see if someone has extra media you could use in a quarantine.

Make sure the media is well cycled or the load in the QT is small so ammonia does not build up. For 2 clowns and a YWG I would use at least a 20 gallon. Ammonia can be very difficult to read so I just make sure my media is well cycled and watch fish breathing very closely. I will test ammonia if I see heavy breathing but will only trust a CLEAR positive or a CLEAR negative it is always really difficult for me. If I see heavy breathing I will do a few 50% water change over a day.

Make sure food isn't settling in the aquarium and you are cleaning the filter often.

Normal rock will soak up medications so it is not ideal for quarantine setups. I use Seachem Matrix media for my QTs but there are other options too.

In my opinion, try to get fish that are small specimens so the smaller aquarium is bigger to them. That could make it easier all around for you.

 

[Schulks]

And I am NOT an expert. I'm just a hobbyist too. I help because I have been there and sometimes the experts have a hard time translating to extremely new hobbyist.

Please find a complete resource from an expert to help guide you through quarantining fish.
I Learned from a hobbyist expert named humblefish. You can still find his resources online.