if they are out and exploring the tank when you're gone but hide when they see you, that means they are scared. you said you only feed on the same corner cuz they think its food. well if they see you and thinks your going to feed them. they should be all over that corner on top begging for food and not hiding. test it out. go to the tank see if they are beggin for food in that corner. if you drop food and they dont go crazy then they are scared.