So just put the old media into the new filter, then put some new media into the old filter so your still selling it complete.
The water holds no bacteria at all worth mentioning, if you add the fish to the new tank without the old media, you will need to be doing minimum of 50% w/c daily for at least a month until its cycled and be putting the fish thru a cycle, which isnt ideal.
Its not just that its only a 48g tank, an Oscar needs a 75g minimum tank, 4ft x 18" minimum, as they can reach 16" or more, thus needing turning space and a 3ft, 14" wide rio 180 is far too small, a rio 300 would be a minimum IMO, extra foot in length, extra 4.5" width. I know its hard not to have your ideal fish, but its always better to wait until you can house them properly and for life rather than making do with an unsuitable home for them.
The water holds no bacteria at all worth mentioning, if you add the fish to the new tank without the old media, you will need to be doing minimum of 50% w/c daily for at least a month until its cycled and be putting the fish thru a cycle, which isnt ideal.
Its not just that its only a 48g tank, an Oscar needs a 75g minimum tank, 4ft x 18" minimum, as they can reach 16" or more, thus needing turning space and a 3ft, 14" wide rio 180 is far too small, a rio 300 would be a minimum IMO, extra foot in length, extra 4.5" width. I know its hard not to have your ideal fish, but its always better to wait until you can house them properly and for life rather than making do with an unsuitable home for them.