4ft tank

Sorry if this is the wrong place to post this question, i'm not new to fish keeping, but I'm very new to keeping my own fish tank and species other than goldfish. My family has had goldfish for 15 years or thereabouts, so since I was 4, and currently we have a 13 year old and 3 year old goldfish...

HI, I have two young Red shoulder severums in my tank around 1-1.5 inches. They are in a 4 ft tank with some smaller south american tetras and are very shy. Why is this? They come out to feed and then go and hide again? I want them to be right as they will be having some geophagus tank mates...