i have 6 guppies in my 2ft platnted community tank consisting of 20+ cardinals and 4 otos , after a WC (bacteria boom after WC don't know why ) i noticed the guppies gathering only at the top corner of the tank , with 1 isolated under some plants ...

after a while the isolated one will swim around as per normal and another guppy will take over the stunted / isolation mode .

i have already noticed 3 different guppies with that behaviour .

Cardinals and oto's seem fine