Looking for root cause help-- all but one cory died.

[Chiz]

Hello,

Super sad to have suddenly lost some of my very favorite fish that have been in an established tank for years. I am looking for help in understanding what could have caused such a crash in a single species in such short order. I posted this in the cory thread as the deaths are cory only, however mods please move as you like.

There is a picture at the bottom that will illustrate how fully planted (ok, overgrown!) this tank is. I've found that Sterbai are the most skittish of any cory I have raised, and these have been in here for years. I do have a 'beach' for them and generally keep that clear. In any event, yesterday I noticed a dead cory on the beach. And then I found another, and another, and 5 out of 6 suddenly died.

I took a water test (details below), and then did an 75% water change. The remaining cory is still alive this morning. Should I move it out of this tank?

Also, I am currently running 4 tanks, another 29, a 20 and a 55. All of them have cory in them, including 5 adult Sterbai in the alt 29g. How do I prevent this issue (whatever it is) from happening to those other tanks?

And lastly, why are the CPD and the pleco OK? You would think that a tiny CPD would be much less tolerant to an out of whack parameter rather than the sturdy 3" catfish, yet they seem fine (and most importantly, still very much alive).

Any help on determining root cause would be very much appreciated.

Thanks.

Tank
What is the water volume of the tank? 29 gallon
How long has the tank been running? Since 2020
Does it have a filter? Yes
Does it have a heater? No
What is the water temperature? 76
What is the entire stocking of this tank? (Please list all fish and inverts.)
6 Sterbai cory (5 now dead)
4 Celestial Pearl Danios
1 Clown pleco
3 nerite snails
Neocaridina (hundreds)

Maintenance
How often do you change the water? 14 days
How much of the water do you change? 33%
What do you use to treat your water? 2 drops Prime per gallon
Do you vacuum the substrate or just the water? No

*Parameters - Very Important
Did you cycle your tank before adding fish? Of course
What do you use to test the water? Master test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.

(Ammonia is usually 0, but of course. there were 5 dead cory in the water, 2 for probably 48 hours or more)
Ammonia: 10
Nitrite: 0
Nitrate: 20
pH: 7.4

Feeding
How often do you feed your fish? daily or every other day
How much do you feed your fish? varies, but not a lot. And the shrimp are always eager for any leftovers.
What brand of food do you feed your fish? Same for years, OmegaOne, bug bites, floating flakes (for the CPD)
Do you feed frozen? no
Do you feed freeze-dried foods? no

Illness & Symptoms
How long have you had this fish? 10/8/2021
How long ago did you first notice these symptoms? yesterday
In a few words, can you explain the symptoms? um, dead?
Have you started any treatment for the illness? N/A
Was your fish physically ill or injured upon purchase? N/A
How has its behavior and appearance changed, if at all? sudden death was the behavior change.

Explain your situation in detail.
(Please give a clear explanation of what is going on, include details from the beginning of the illness leading up to now)

Obviously not an emergency, because they are already dead. Trying to figure out the root cause.

 

[Sewerrat]

You mentioned changing 75%of the water if the parameters between new water and tank aren't the same it could cause some deaths with a larger water change. Once a couple die ammonia would be enough to finish off the rest.

 

[Chiz]

You mentioned changing 75%of the water if the parameters between new water and tank aren't the same it could cause some deaths with a larger water change. Once a couple die ammonia would be enough to finish off the rest.

Thanks, but you misread that. I did a 75% water change AFTER the deaths, not before.

 

[Chiz]

Ugh-- no advice from anyone on this whole forum?

 

[Lucy]

Hi, I'm so sorry about your fish, it can be devastating especially losing so many and haven't gotten many replies.

I moved the thread to the disease section. Maybe that will help.

Looking at all the information in your first post it appears that everything was in order except for the ammonia, and I kind of wonder if that would jump to 10 so quickly.

There's not much to go on when there are no symptoms, no marks to go on, just a description of being dead.

Obvious questions would be, are you sure you used water conditioner with a water change or possible contamination.

Unfortunately, we are often left with the only answer being, huh, I wonder what happened.

 

[Chiz]

Thanks very much Lucy. I didn't think to take pictures of the dead fish as they didn't show any obvious signs of distress.

As for water changes, I age new water in 16, one gallon jugs, mostly for temperature acclimation. I add one or two drops of Prime with a dropper to each gallon before adding the water to the tank. This tank had its last water change about 10 days previous, and I use the same method for all for tanks and have done so for years. If I had happened to miss prime, you would think that the CPD or snails would have been affected, and most likely right after the water change. Airborne contamination of some sort is possible, but unlikely, as this tank is the only one of my 4 that has a lid, but again, why just the cory and none of the other inhabitants? I don't even see a single dead shrimp. I am at a loss and worried that a similar event will plague one of my other tanks without warning.

No one has offered any suggestion on what to do with the remaining cory, who is eating well and looks perfectly healthy, so I have left it in the tank. I've starting looking else where for info and I guess I can update this group if I get some insight as to what caused the sudden cory deaths.

 

[Chiz]

OK, I just don't get it. "Driftwood tannins" has more than 50 replies. "why are my CPD hiding" had someone helpfully post the emergency template. I've been a contributing member here for over two years now, but just can't seem to join the community, whatever that is. Admins, please delete my account, I can't seem to find a place to do it myself. So long everybody, I'll move along.

 

[FishyChaos]

OK, I just don't get it. "Driftwood tannins" has more than 50 replies. "why are my CPD hiding" had someone helpfully post the emergency template. I've been a contributing member here for over two years now, but just can't seem to join the community, whatever that is. Admins, please delete my account, I can't seem to find a place to do it myself. So long everybody, I'll move along.

I've been following this - and I would reply, I just don't know. Too inexperienced. Sorry you're struggling, though. I wish you and your fish the best.