yes, but if he plans to leave the others in the 29 gal, removing the filter will throw him into a mini cycle.
ok, you dont give information in wether or not you know about the Nitrogen Cycle. In case you dont
http://www.fishlore.com/NitrogenCycle.htm
also do you have a test kit to measure tank parameters? The API test kit is the one recomended here.
the best thing to do is the following:
squeeze the old filter into a cup (there will be green liquid comming out) and get some gravel from the old tank. Once the 55 gal is running with dechlorinated water, add the gravel, and then add the green mud directly into the new filter.
get some household ammonia with no additives and/or surfactants. and add as many drops as it takes to raise the ammonia to .50 in the new tank. repeat the proccess of ammonia adding every day until the the new tank test for 0 in both ammonia and nitrite and your new tank is ready.
this is the only way to do it without compromising either tanks inhabitants.
good luck and welcome!