I just saw some hardwood flooring on sale that I really like, but it would mean moving my aquarium long enough to get the flooring down under it.

It's a 72 gallon bow-front with tropical fish (dwarf powder blue gouramis, a 9" pleco, a brazilian ram, rosy barbs, a couple bosemani rainbows, 5 cory cats, a bunch of tetras of different types, et cetera).

I have a 16 gallon tank upstairs but it has and algae eater, an upside-down cat and 2 angels that probably wouldn't welcome the company. How much trouble would it be to move this tank temporarily? How much trauma to my fish?

Don't try to move the tank with any thing in it as it might break the seal. That makes it a bit of work to take apart the tank and put it together again but I don't think it will stress your fish too much. It is only a problem if you have very shy or sensitive fish.

I recently moved a 75 gal tank from one wall to the opposite wall. I put water into a 20 gal that had nothing but water in it and put my fish there...about 45 total with 50+ fry. They were only in there for a few hours.

I took my tank all the way down to the gravel and moved it like that. Filled it and waited until the temp leveled out and put the fish back in. You don't want to strip it down to far or you may start your cycle over again. I saw .25 of ammonia on the second day and then it was gone and so was any hint of a cycle - I was lucky though.