Guppies Dying In Quick Succession

[KatieB1991]

Tank size: 54l

tank temp:25 degrees c

Fish Symptoms: not many Symptoms, raised dorsal fins, rubbing against ornaments etc.

Volume and Frequency of water changes:30%-50% water changes per week

Chemical Additives or Media in your tank: none

Tank inhabitants: currently, 7 Guppies and 2 Albino Corys, Was before death, 2 Endler Guppies, 10 Guppies and 3 Corys

Recent additions to your tank (living or decoration): Recently added, 3 Corys about 2 weeks ago, then a week ago, 3 new plants and 2 moss balls.

Exposure to chemicals: none

If someone could help would be grateful!
I woke up this morning and found 4 dead fish, with no obvious symptoms? i have treated the water for parasites to see if this is a problem?

 

[Spurry]

you need to post your water parameters before you can get any help so water condition can be ruled out
the flicking thing can be nothing to some sort of irritation hence needing to know the water parameter
also how long as the tank been running