Just an FYI use a power head in your QT too. I Had to hypo all my fish from my DT 5 weeks ago. I had 2 true percs, 1 purple FF, a royal gramma and a tiny neon goby. I did exactly as you did, took 6 gals from my DT added it to my QT, hang on filter and heater. I took 48 hours to add the remaining 4 gals of fresh RO Water to get my salinity in Hypo. Unfortunatly one perc never made it past the transition. Then 3 weeks later I come home to 2 more fish dead and one on its way. I have been doing every other day water changes of 1 gal to help with the massive bio load on the 10 gal tank. Buffering the water letting it circulate for days so its stable. All my levels checked out and then I realized I didnt have a power head in the tank. It may not of been the whole cause but after I added it my royal gramma seemed to respond, look and act better.