The frogs you got more then likely underlying issues that were to early to catch at the time and the problems or sickness eventually got to them causeing them to pass, it was more then likely nothing you did. I to got my first pacman frog from petsmart and it passed from edema from being kept in too cold conditions. And I spent tons of money trying to save it with no luck. Even if you leave the water out like mentioned you should add some Reptisafe or something similar to be safe, I don't think this is what your frog passed from though because he would have got toxed out syndrome which is very noticeable. They swell up like a balloon and to treat it you just drop him in some clean water for a few hours changing up the water when it cools and they eventually go back to normal. I don't know if they sell single frogs or only wholesale but Sandfire Dragon Ranch produces some very nice and healthy frogs and so does the Frog ranch, the frog ranch was the first place in the states to breed the albino successfully back in the day and Sand fire was the first to breed and produce quality Catinga's. These guys Know what they are doing and have been doing it for years, I just don't know if you can buy individual frogs and you would have to get it shipped. I know Sandfire goes to some of the expos in the states but not sure about the Frog ranch. The guy here at my reptile shop gets wholesale from The Frog Ranch and all 4 of my guys/gals are healthy as can be, the oldest female is going on 5 years.