I have a 55 gal tank with 2 oscars 2 dempseys a large pleco and a really big kissing gourami. They are all full grown and are quite nice to each other. My oscars have holes in there heads though.
you can put a garden hose from one tank to the other and then suck on it. You may have to have the 180 gal a bit lower to get a vacume going though. After you get that water in there just add tap. It should be a good enough mix to get the chlorine out. Just keep in mind the temp. I always add a...