Minnow swimming sideways

[Renren01]

I bought a 125L tank and set up on 21st November. It has a fluval u3 filter and a heater which is at a steady 26 degrees. A week later on 29th November I introduced 3 silver and 3 gold minnows. Yesterday, 3rd December I woke o a dead fish (gold minnow) and today to 2 more (1 gold and 1 silver). The previous night I had noticed the tail of the silver had closed and the fish was struggling to swim. The gold one was swimming at the surface constantly. Today I have a silver one which is swimming at a slight angle. His head tilts to the right.
I have done Nitrate, Nitrite, ammonia and PH water tests. All have come back in the normal parameters.
I'm just not sure why they are all dying and showing such different symptoms.

Can anyone help?

 

[Delapool]

Hi, normally cycling a tank fish-in takes a month to two months. Unless helped along with borrowed filter media, etc.

I'd test your tap water to get a base line and then get a lfs to test your tank water to check your test is working properly. The instructions have to be followed exactly unfortunately.

If it is not water chemistry, then unfortunately multiple deaths like that suggest a bacterial infection.

 

[platylover26]

The tank is uncycled and the fish are getting Swim Bladder Disease.. +1
For the post above