Ive set up a new fish tank and ive put a fantail and two corry cats into it i was wondering if i could put one of the corry cats into my 21.7 gallon tank with my three fantails

Cory Cats are fish that prefer to have their own company and therefore happiest in at least groups of three or more. Although there are quite a few on the board that do keep Cory Cats with their goldies,a much better selection would probably be a Bristlenose,or even a couple of Dojo's.I'm not saying that you can't use the Cories,I'm just saying that a) if you salt your goldfish tanks,they don't handle salt so well,and b) a few people have had problems where their bigger goldies tried to eat them for dinner.

i dont salt my tanks but people told me corrie cats were fine with goldfish

Im with Devs on this one, Cory cats dont get very big but as the goldfish grow the mouths get bigger and bigger and its amazing what a goldfish can swallow. Im sure you dont want to be posting in emergency about a catfish being stuck in a goldies mouth and the spines of the cory caught.
Best to keep them seperate.

I have 3 albino Cory Cats in with my goldies. I have not had any problem there at all.

My daughter has cories with her goldfish but her goldfish are small. When the goldfish get bigger the cories will go in my tropical tank to prevent any accidents happening.

I have two cory (bronze ones)-Whiskers and Cory , in with my goldfish. They get along very well. They seem to be doing well in the unheated tank with them. They are also very fun to watch. My favorite thing they do is what I call "the catfish dance" Where they swim rapidly up and down the side of the tank wiggling as they go. They also like to to half flip over half way and immediately right them selfs again. My calico fan tails also likes to occaisonally go over and hang with them once in a while

Oh yeah by the way I do salt my fish tank and my bronze corys are just fine with it.