It will hang out on anything, glass, powerheads, plastic, your heater. But hopefully where it can colinize the best like in your filters. Its always best to have something for your fish to hide in when in QT, some people use PVC pipe which the bacteria will cover that too.
If treatement is ongoing and you remove the sponge with the bacteria then this is why you are doing water changes from the main tank, to use some water that has been processed and clean.
Thomas