Oh I thought seeding a tank meant that once you put the filter media from a mature tank to a new tank that the bacteria would colonize on the decor and gravel and stuff and would be ready for fish in a hour or so.You asked about seeding. This is usually done to give the filtration a jump start before doing a fishless or live fish cycling of a tank.
In theory, and in practice by my experience, you can take half the fish from a cycled tank, and half the filters or media, and add them to another tank to have a second cycled tank. I do this with bare bottomed tanks on a regular basis, if you have gravel or another substrate you will have to take this into consideration.
Tolak
But wouldn't the bacteria that isn't being used die off with only one fish in it? Or is the pleco considered mulitple fish because of how much waste it produces? After I take half the media from the 20g and put it in the 55g filter should I wait like half an hour before adding the pleco to give the bacteria a chance to spread out through the tank? Or could I use the filter that comes with the tank and take the media that comes with it and stick it in the 20g for a couple weeks and then stick it in the filter and add the pleco?By looking at the 20 gallon you have with the plec & 8 tetras, you could take half the media from that tank, put it in the new filter on the 55, & add the plec. Wait a week, & add the angels, as long as they are small.
I use non-standard media in filters all the time. I have whispers, tetras, a hartz, & some others with aqua clear sponges cut to fit. If you can squeeze the cycled media in, it will work, as long as it isn't so dense that it impedes water flow.
Tolak