Corydoras randomly dying, any ideas?

All posts regarding the care and breeding of these catfishes from South America.
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Posts: 113
Joined: Wed Apr 14, 2021 12:28 pm
My cats species list: 3 (i:2, k:3)
My aquaria list: 1 (i:1)
Spotted: 4
Location 1: Linkoping
Location 2: Sweden

Corydoras randomly dying, any ideas?

Post by Woodh »

I got this group of 7 CW009 a couple of months ago. Originally I had some problems with one which I thought to be septicemia, it made it through and everyone has seemed to do well since. Up till two weeks ago that is, I found one dead in the morning figured it was probably the one that had problems initially and that it simply had some kind of damage from that.

Two days ago I found another one just the same, I couldn't see any signs of sickness, the rest eat and move around as usual. The two dead fishes just seemingly dropped dead on the spot and showed no signs the day prior and didn't seem to have lost any color(even in death). Measured water daily the days after and saw nothing out of the regular- well cycled filter(s) no ammonia or nitrite and low nitrates. I have seen them flashing the odd time and I feel like they have gone up for air more than my Sterbais- if that's indicative of something I don't know.

I have thought about it quite much since it's the first fish I lose since coming back to the hobby almost a year ago, time moves fast.
The reasons, although I don't find them very convincing, I could think about are either- That the planting substrate(fluval stratum) I used under the sand leeched something into the water but the tests have never showed anything or the the fact that their tank is quite close to a window. The weather has changed so there might have been larger temperature flucations(have the heater set to 24 degrees~ but I suspect it might have dropped to the low 20s a night or two).

Yesterday I moved the remaning ones into a larger aquarium where I have had zero problems so my fingers are crossed that they will make it but it still irks me that I can't really pinpoint what the problem is. Kinda wan't to go and get a couple of more since 5 corys seems a bit to few for a school in my mind, what's your opinion on that- honestly though they don't seem to care that much about it and move about as usual so might just leave them as 5 for the forseeable future. Do you agree that it might be a temperature related issue, any other ideas?

I also wen't back to where I got them from to ask if there had been any problems with the ones remaning/complaints from other customers but he incisted there had been none.

Have a nice weekend!
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