Is My Tank Overstocked?

[mandalay]

hi guys!

i'm new to the fish keeping so not quite sure what to make of this...
i had 5 guppies (all male), 2 platies (both female) and ADF in my 40 Litre tank for about 4 days and they all seemed to get along fine. then i added 4 cardinal neon tetras and all my guppies strated to all behave very erraticly/stressed and agitated... but towards each other not towards cardinals or anyone else.
why is that? have i overstocked my tank and gave my guppies to little space? so they feel like they are in each others' faces all the time and becoming more aggressive?

p.s. its a new tank, it had a fishless cycle for 2 weeks before any fish been added to it at all. i've for api test kit and all my chemical processes seem to be at bay. ammonia rises slightly every once in a while but i've got ammonia remover that i apply.

does anyone have any idea on whats going on with my fishes? why are they suddenly so cranky?

 

[N0body Of The Goat]

Very overstocked, you have ~50cm of adult size fish in 40l of water, your stocking would be more in line with a 3-foot ~100l tank (esepcially after boosting the numbers of Cardinal Tetras, 4 is not ideal, they are social fish). This will create stress and lead to illness/fighting. even before we talk about how such a small volume of water can quickly become toxic soup in the blink of an eye.