I agree with amazon, keep your filter media seeded in another tank until you need it, and fill the QT tank with 50% tank water/50% new water. I don't use sponge filters, I keep an extra sponge in all my HOB filters and pull one out when I need to set a QT up.
And L144's are extremely sensitive to the presence of ammonia and/or nitrite in the water. Nitrite can be more deadly quicker than ammonia. They don't breathe air. What happened was it's gills got burned from the elevated ammonia/nitrite and it couldn't breath. Sorry that you lost him.