Help with my tiger barb?

okay i had 1 tiger barb in my 20 gallon tank with my two gourami and 4 tetras and 4 guppies but i had to move him bcuz he was attacking them so i had to move him into the 55 gallon which i have 2 jack dempsey cichlids in there and one convict cichlid but the cichlids are bulling him badly.... the only choice i have his to move him into the 6 gallon tank... is this enough room for him? can i put 2 other tiger barbs in there with him? thanks for any help