Hi, I have a question to ask those experience with cardinal tetra.

My Cardinal tetras have been dying off recently, after they have been growing healthily and has increased in size. (I have kept them for around 3 months, and most of them are around an inch in size now, from 1.5cm)

Over the past two weeks, more than 10 has died, overnight with no signs of stress.

Below are my tank parameters.

4x1ftx16inch(h)

143 liters
Canister filter

Tank cycled and running for close to 4 months alr.

Only dosing flourish

Nitrate: 10ppm
Nitrite: 0
Ammonia: 0
pH: 6.5-7.0
Gh: 10 drops API
Kh: 2 drops
Temperature: 27-29•C

Gh was previously 8 drops and all Cardinal are fine.

I'm running a CO2 system with t5 light, running at 8 hours a day. One hour before light on and off, CO2 will be on.

I have the below fauna:
11x rummy nose
6x glow light
35x Cardinal
5x Gold tetra (added recently)
3x juvenile SAE
5x Yamato shrimp
10x cherry shrimp

I'm puzzled with the sudden death with no prior symptoms. I had one with bulging eyes and I had removed from the tank immediately, not sure if dropsy is contagious.

I suspect it might be overstocked, since previously they are all small. My tank is heavily planted.

Hopefully someone experienced out there can offer some advice? Thank you in advance!


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