All My Fish Are Dying!

i think my fish have fin and tail rot but im not too sure!

two days ago i had 10 tetras and i found most them missing their tails and dying vertically in my plants.

this morning i went to the local aquarium and took the tetras.
he tested the water and it's perfectly fine, and he concluded that another fish must have eaten the tails,

however i only have guppies and corys in the tank with them! since this morning my three remaining tetras have died too!

now im noticing my corys panting heavily, not eating and with fraying on the fins
one of them is even lying sideways on a plant panting to death!

i feel so bad for them, but it's the middle of the night and the weekend and i dont know what to do..

PLEASE HELP!!!!

Do you think their fins are getting caught in anything? ie. The filter?
Do they just fray on their own?

just on their own.
see how the panda is sitting on its side.. it's been like that for hours now just panting away
it also doesnt move when the other fish go and have a prod
it hasnt come up for air either!


i feel so bad for it.

is there anyway to humanely kill fish?

With clove oil but don't go euthanising yet we may be able to say them,

Did you cycle your tank?
What are your water stats?
Have you used any cleaning or airosol chemicals around the tank?