Guppy Help

[TommySide]

Hi,

I have got some guppies (got them 3 days ago), i've had guppies before and unfortunately they all died. i've just lost another one from the ones i got the other day. my water readings & temperature appear fine, i'm really at a loss as to what i'm doing wrong? the only thing i can think of is the food & amount i give them.
the one that died just now seemed to plummet to the bottom head first really fast. anyone have any ideas what im doing wrong and why fish just cannot live under my keeping?

thanks

 

[Truck]

have you cycled your tank? and can you post the water stats?