What temp. Do you keep your tank set at ?
Yesterday I transferred several fish from my 82 degrees, QT tank to my 78 degrees, display tank. Transferring fish from warmer to noticably cooler water is not a good idea. Prior to the transfer, I did a big WC on the display tank, adding warmer water, which elevated the temp to 82 degrees. The fish, which include Hardy Tetras, Cichlids, Loaches & Plecos were not adversely affected by the 4 degree increase in temp.
You've got to keep rapid temp increases within reason, but say your tank is set at 78 degrees, a 50% WC w/83 degrees new water will only bump the temp up 2 or 3 degrees. No big deal unless you are breeding delicate species.