marko - get an AquaClear HOB filter and throw it on the back of the tank to filter the quarantine water. Take the filter pads from the hob and throw them in your "display tank" or display tank sump for a couple days to start accumlating the beneficial bacterial. Do a water change in your display tank and throw that water into your QT tank and put the filter pads into the HOB. You should be good from there
Bioballs are too much work to keep clean.
once you are done with the QT you can just empty the tank and throw out the filter pads. When you need to QT again just put some new filter pads back in your DT and reapeat the process i mentioned above.