Here the time line.
Brand new QT:
10g, Aqueon 10g power filter, AquaClear 10g Powerheads, 2 pvc
pipe, 50 watt blue color light
I placed the filter media to my DT (7 weeks old) two days before hand. On Saturday I added 5g of water from my DT and 5g of new water. I got a firefish the same day and acclimated her with floating the bag method (for good 1.5 hrs). The same night I feed her some frozen brine shrimp which she ate. The follow morning i done a water check and everything was good. She hiding behind a pvc
pipe, and notice she was not as active as before it was pretty earlier so i assume she sleeping. Try feeding but she didn't go for it. Later afternoon found her staying out in the open at bottom of the tank couple hrs later she dead.
I fish her out of the tank and checked the water once again, and everything turned out ok. It summer here and my house don't get below 76 F during the night or over 80 during the day. So I don't know what did I do wrong, please advise.