Sorry to hear about the little one. I'm surprised that Petsmart sells GBRs, as their fishkeeping practices aren't conducive to keeping them alive long enough to sell them. Mine only sells Bolivians.
It sounds like your water parameters are good, so hopefully you'll have better long-term luck with the other one. My (unsolicited) advice would be feed a varied diet, don't overfeed (a fasting day helps), keep your nitrates under 15 ppm
, and match your water temperatures as closely as possible when doing water changes. (I use a 25 W heater to adjust my fresh water to tank temperature overnight.)