Dont know why fish died

[Llama_13]

Hi !
I fed my fish 2.5 hours ago (I feed them at 4:00, it's 6:30 now)
And I just stopped to watch them for a bit and I could only see 1 of my golden fluorescent Danios (I have 2). I went in for a closer look and I found the other one at the top of the tank dead. I checked- it was definitely dead. I saw both of the golden Danios when I fed them earlier, and they both looked okay.

I don't know how or why it died, as it wasn't trapped/stuck in any way, and yesterday it had been showing normal behaviour. However, I did notice that it looked like it had its tail and fins chewed off 0.0

I'm really worried about the safety of my fish, so please reply ASAP!!

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In my tank I have:
3 Leopard longfin Danios (one seems to be more dominent than the other Danios)
1 remaining gold fluorescent Danio
6 Widow fish
2 Zebra Loaches

I also have a lot of (plastic) plants and places for the fish to hide in if needed.
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[Delapool]

Nothing on your hands that could of transferred to fish food?

[V227]

Relax, As long as your remaining fish are acting in a normal manner and you don't observe any signs of a disease outbreak, you can just write this incident off as an unexplained death.
Sometimes things like that happen. Every fish keeper at sometime or another comes home to find a prized fish deceased for no apparent reason.
Probably nothing to worry about.

[Autumnsky]

First off, what are the water parameters?

Maybe your parameters are not within safe levels?

Anytime there is a fish death, do routine pwc or two in the following days. It is just a normal task to do after a death.

Fin errosion can also be a sign of water problems.

[Llama_13]

OMG PLZ HELP ASAP
i just looked and one of my widow fish is dead
PLZ PLZ help im really worried
i am literally freaking out
my fish were all fine earlier
help im really worried

IT DOESNT LOOK LIKE IT HAS AND DISEASES
I THINK IT MIGHT BE WATER ISSUES
I DID A CYCLE ONLY LIKE 4 days AGO

IDEK
ITS IN THE SAME PLACE AS THE PREVIOUS DANIO
DO YOU THINK THEY GET STUCK?
OR IS IT JUST THE CURRENT FROM MY FILTER
ITS IN THE CORNER BETWEEN THE HEATER AND THE FILTER

im going away for a week in august
what should i do
IM SCARED TO LEAVE THEM

[TMaier]

Is your tank established? As in 40+ days of building beneficial bacteria?

Test your water. What are the parameters?

[Llama_13]

No, it wasn't established

Parameters:
Hardness-150
Chlorine-2/2
Ph-6,3
Alkalinity-30
( ^Probably not very accurate)

[DreaminginBlue]

Do you have a kit to test for ammonia, nitrite, and nitrates? That's probably where your problem lies.

[TheSmallFish]

You said it was stuck between the heater and the filter. I have had bad experiences with fish and good filters. So to stop that I just put a sponge around it.