Unexplained Fish Deaths in Quarantine Tank

[dedvalson]

Hi all,

I have a 45 gallon quarantine tank that is permanently set up with a wet dry filter and a protein skimmer.

I use it for fish (not for inverts) and till now it has really just been an observation tank (haven't needed any treatments).

A few weeks ago I introduced a Bullseye Jawfish to the tank. Prior to that the only resident was a Blue Spotted watchman goby who had been in the tank for about 8 weeks.

At the time I introduced the Jawfish I changed the substrate from a thin layer of black silica (really just there for appearance) to a thicker layer of medium aragonite so that the Jawfish could dig. I wasn't concerned about losing any biological effect of the old sand because I had the wet dry and the previous layer was really thin. I washed the aragonite very well and no clouding was introduced.

Both the jawfish and the watchman goby were doing great. Their appearance was normal and the jawfish was busily digging under rocks and building tunnels. They were both eating well, devouring all the frozen mysis, pellets and live brine I gave them. Then one morning (about 10 days after I got him) the jawfish died overnight. The body looked totally normal. No injuries, no spots, nothing visible externally.

I tested the water and found nothing out of line (measurements below).

I couldn't understand what he died from but I didn't do anything at that point since the watchman goby was still eating well and acting normal. About a week after the jawfish died, the goby died, also overnight.

This had me very concerned so I tested the water again and once again everything looked good. I ran a heavy load of carbon for a few days and some purigen to try to remove any pollutants that might be present.

I wanted to know if the tank had issues without risking any valuable livestock so I purchased 5 small Blue Green Chromid Damsels from the LFS and put them in the tank.

They all transferred in great and started eating within hours. Like the other fish, they appeared completely normal, swimming around and eating everything I fed them.

After about 6 days, one of the chromids died overnight. I had observed all 5 eating well just the evening before. Since then, I have had a succession of deaths, roughly one every 5-6 days. In every case, the fish is eating great in the evening and dead in the morning.

I am now down to just 1 chromid and, like always, he appears healthy and is eating well.

I have examined the fish closely for any external signs of disease and I can't see any.

Water Conditions are:

SG 1.024 (Red Sea Hydrometer)
pH 7.8
Temperature 79.6 F
Ammonia 0 (Lamotte)
Nitrite 0 (Lamotte)
Nitrate 3 PPM total Nitrate (Lamotte)
Phosphate 0.4 PPM (Hanna low range checker)
Alkalinity 11.5 DKH (Hanna and Salifert)
Calcium 348 PPM (Hanna and Salifert)
Magnesium 1350 PPM (Salifert)

The nitrates would be high for a reef but they seem OK for this fish only QT. The only thing that concerns me is the pH, but that has always been low in this tank.

Have I missed something? I am trying to think of something to do next. I am considering sterilizing the tank but would prefer not to kill the wet dry. But if I can't think of anything else that is what I will have to do.

What could kill one apparently healthy fish overnight and leave all the others?

Thanks,

Don

 

[JustinM]

It’s a good practice to sterilize qts after each batch of fish. You may be dealing with something bacterial. I would advise to get rid of the wet dry and have a simple setup.

 

[Jdub968]

No other symptoms like heavy breathing flashing scratching lethargic swimming into the currant of a pump ect? There's two things that come to mind it may be possible that there was something in the old sand and you disturbed it a mycobacterium. The other would be the jaw fish was carrying something like velvet. If there are no other symptoms I would do as Justinm suggested and tear down the qt sterilize everything and restart it with a simple sponge filter no gravel no rock. This makes it easy if you ever have to treat with meds or chemicals the wet dry filter provides a lot of surface area for parasites to attach.

 

[dedvalson]

I really have looked close and do not see any external symptoms. I have seen velvet before and that is certainly not there. The only behavior change I have noticed is that the chromis seem more active than normal, swimming pretty fast around the tank. The two forks of their tail are often together instead of apart like I usually see them. But all of them have done that since I had them.

I guess I am going to have to tear it all down as you suggest. I am sure glad I had a quarantine tank!!

Any suggestions on how heavy duty of bleach solution I should soak everything in? I figure I will just fill the tank itself with a bleach solution and put everything in it. How strong do I need to go?

Don

 

[Jdub968]

When fish are showing hyperactivity like you mentioned swimming fast and hyper, this is a sign of osmotic shock it can be brought on by a fast temp change, arras tic ph swing or change, I'm sure there's other things as well. Have you checked for stray voltage? I've had fish die of osmotic shock after a ttm and I could not find anything wrong temp SG ph were all correct so stress may also be a contributor to osmotic shock. Here's a sterilization chart just make sure to use regular bleach and keep in mind the drying process is really the key factor to sterilizing

 

[lagatbezan]

It’s a good practice to sterilize qts after each batch of fish. You may be dealing with something bacterial. I would advise to get rid of the wet dry and have a simple setup.

This is what I would suggest as well. I would dump all the sand and any filter media out for good and disinfect the tank and all equipment with bleach/water solution and then let everything fully dry for at least 24 hours.
Also agree that there is no need for the wet/dry or even a skimmer on qt.
I also know that what you experienced with the chromis "might" not be disease related. They have a social order in which they always pick on the weakest one in the group specially at night when the light goes out and they are looking for their own place to sleep. This competition and picking among them usually results in what you experienced and ends when there is only one left.
few people have had success keeping a group of them alive together in larger display tanks even harder in smaller qt.