Within a week 4 fish dead help

[Dyood]

I have noticed on all 4 fish they have had their fins bitten off but I can't figure out which fish it is I lost a female betta, a blue eyed yellow rainbow, a black cory and a female swordtail.

The other fish I have in my tank are,
1 male swordtail
4 females and a load of fry
1 male platy
2 female platy
2 blue eyed yellow rainbow
1 celebes rainbow
2 dwarf neon rainbow
1 panda cory
2 peppered cory
2 bronze cory
1 black cory
1 gold cory

I know they all work together, I know some should have more but these fish have been rescued and taken from friends and family who could have them anymore,

I have majority of them for 6 months except and black and gold cory for 2 months

Please any ideas on who is the aggressive one and killing off my fish.

Could this also be a reason why my platys arnt breeding

 

[Crispii]

What tank size are you keeping the fish in? How long did you set up your aquarium? Ammonia? Nitrite? Nitrate? GH?

 

[Dyood]

Tank size is 400 litres or 87 gallons I think around that, I just did a 75% water change, but

Ammonia was 0
Nitrite was 0.2ppm
Nitrate was 5ppm
Ph was 7.3
Forgot to check the gh

 

[JuiceBox52]

If you could get the GH for us that would be great

 

[Dyood]

If you could get the GH for us that would be great

I will but as of now is there any thing else that is popping out at you on who could be the aggressive one

 

[JuiceBox52]

I cant think of anything right now. Could it be fin rot?

 

[Dyood]

I cant think of anything right now. Could it be fin rot?

I thought of that but there was no signs whatsoever of fin rot

 

[JuiceBox52]

Well, whether it is fin rot or was bitten, large water changes will help them heal

 

[Dyood]

Well, whether it is fin rot or was bitten, large water changes will help them heal

Thats why I did one the other fish don't have signs or damaged fins as of now

 

[JuiceBox52]

Did you notice the fins before or after death? How fast did the fish die after you noticed the torn fins?

 

[Dyood]

Did you notice the fins before or after death? How fast did the fish die after you noticed the torn fins?

I noticed before the recent one the black cory was within a 1 day the betta on the day of death within a few hours same with the blue eyed rainbow and the swordtail was 2 days before death

 

[Colin_T]

pictures?

 

[Dyood]

I have found the culprit one of my female swordtails is doing it for some reason, she's been separated and no more issues has occurred