Should i transfer my glowlight tetras?

i have 5 glowlight tetras mixed in with platy and harlequins.they are the smallest of the fish in this tank and have had them longest and they are acting timid now..they just stay in their own corner and dont really swim all over the place anymore they eat and all but stay below the midway part of the tank..should i move them to the new tank(20 gal) i have?there are no fish in it yet..it has been up running like 3 weeks