Have you got a nitrite reading? Nitrates sound a bit low unless a water change has just been done. Mollys really prefer brackish water (or very hard alkaline water, which you don't have from your pH reading) or very very clean mature tanks, so I wouldn't be at all suprised if they don't do well in your tank.
djceri_g said:
the problem is Pet smart i bet! They are horrendous, every fish I have bought there has died within a week! also, has killed my other healthy fish! Never Again! Maybey the pleco was hungry, when I had a new tank I fed mine with algae wafers. Sory to hear about the loss though! Just don't let this put you off keeping fish
No Petsmart in England, though from what I've heard, Pets at Home is sort of the equivalent from what I've heard. The fish aren't likely the direct problem here (though disease is common in stores like that, fish purchased from such places really need to be quarantined) rather the advice given for starting up a new tank (actually, the lack thereof.) A starving pleco would be very skinny, from the picture I saw of this pleco, he was perfectly normal. They're also very good scavengers, I'm sure he was getting food.
little pleco baby hunny bun.. 
