Fish dying

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SaraB

Aquarium Advice Addict
Joined
Nov 13, 2018
Messages
1,610
Location
Ontario Canada
So i've had my 55 up and cycled and running with fish for months. After my one Molly got sick i decided to rehome the other 2 and replace with a school of 10 black neons. Everything was fine. A couple of weeks later I added 5 otocinclus and as predicted i lost 1 within a week but the other 4 were happy and healthy. On sunday I added 6 cardinal tetras and this is where everything went downhill. My total stocking at this point was 10 black neons, 3 female platys(+fry), 6 cardinals and 4 otos

Wednesday: wake up to find 2 dead, did a small water change and went to the store to replace them. Added 2 more female platys because mine were getting shy.
Thursday: wake up to find 2 more cardinals dead. Went back to the store and instead of replacing them i ask if i can get a plant instead (he was nice and let me)
Friday: wake up to find an oto dead
Today: Wake up and found another oto and cardinal dead. Finally had time to get my water tested.
Ammonia 0
Nitrites 0
Nitrates 0 (surprised me)

So I don't have any nitrates showing up. Is my tank going through another cycle killing off more sensitive fish? I did just replace my filter from a HOB to a canister.

OR

Is my tank too understocked to produce the necessary amount of waste for nitrates to show up? Are my water changes too big (approx. 50% a week)
 
Sounds like an illness going through the tank from the more recently introduced fish.

Do the fish seem to have any physical tell tale signs?

QT tank is always a safer bet.

Do the fish seem to be breathing faster than normal, have grey or brown or flaming red gills? and discolored spots, patches, tiny salt looking specs?
 
None of those symptoms, the black neons even let them school with them. I didn't have a separate at tank set up due to lack of room. I'll be setting one up as soon as I get my betta tank emptied and cleaned. They are impossible to catch in the 55 as well.
No fish have died since Saturday.
I think with the cardinals he must have just got them in the store and I bought them before they had time to acclimate to their tanks before going into mine. I have 3 surviving cardinals doing great.
As for the otos, I don't know, I seem to have bad luck with scaless fish.
 
Otos are sensitive to the transporting process and acclimating to the new environment.

They could have been through 4 changes from the origin wholesaler, to the middle man seller, to the fish store to your tank. That's a ton of stress!

My last group had lost all the fish I got at one store one by one, even though they seemed to be eating. My previous 2 purchase survivors seem okay. But they are still in QT. Frustrating though for sure.
 
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