Ammonia level: 0
Tank has been running since Mar 16
46 Gallons capacity
Contains 1 baby black moor, 3 small comets, and a loach.
I have an Emperor 28-something filter with biowheel.
I change the water about 25% every 2 weeks
I add dechlorinator and sometimes PetCetera general aid.

My problem:

I just got my last fish, the baby black moor three days ago. He's about two inches long from mouth to tail. (tiny lil fella!) He was in the pet store pond with a bunch of koi and large comets. He seemed very healthy and active, which is why I bought him. But ever since I got him home, he's been hiding at the bottom of my tank, inside a house ornament and seems afraid of light. My comets have been avoiding him. It's almost like they don't like the lil guy cuz he's black? (lol) but the loach seems to have cozied right up, as the moor's been sharing his fav hidey hole. I've gotten the moor to eat, but I had to corner him and feed him from my hand. I think it's a good sign that he'll accept food.

Is this just new tank stress? What's going on?

i think so
i have read on here that the fish will take some time before they get used to the tank... Did you QT the fish? was he ok in there?

Hi,What are your Nitrite and Nitrate readings?
You may have already realized this from reading the forum,but it's not advisable to house Comets/Commons with Fancy Goldfish-especially Moor's for they are prone to having vision problems.Commons/Comets are much bigger /sleeker/faster swimmer's who tend to hog up all food that can be found.They also need even more recomended room than Fancy Goldfish-normally between 15 and 20 gallons a piece because of the size that they reach and their huge amount of waste that they produce.
I'm also concerned that your filter may not be quite big enough for the filtration that Goldies need-for cleaning up and aeration in the tank.
Is he showing any obvious signs of distress,such as frayed /clamped fins,white grains of salt on him/white patches,etc?We really need full water params to know which way to go from here.If you don't have the complete test kit,your LFS will do it for free.

Yes, please get a test kit for nitrItes immediately. Your tank is still cycling and would be right in the middle of the nitrIte phase.

Bottom sitting and lethagy are symptoms of nitrIte toxicity and some fish are more sensitive to it than others.

In the meantime I suggest doing a large water change of around 50% to reduce any nitrIte levels.