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Yes, goldfish are social and enjoy tank mates

Unfortunately a 5 gallon tank is about 15 gallons shy of what a moor will be happy and thrive in.

You're right to question whether another would fit comfortably in there. Your moor is going to get Large and need more room very soon

They're one of the dirtiest fish to own and need double the filtration of the size of their tank with cycled water before even being placed inside or you're setting yourself up for all kinds of problems and illness

Well the blak more grows pretty big and if you ad more goldfish in time you will hav2 get a bigger tank. The smaller the tank ya it will Stunt their growth but not stop it. Plus pending on what type of fish friend you will ad they grow large too, also black moors are not like social fish no goldfish really is, they all just Do their own thing. I have a 100g with alot of Comets, black moor, fan tails, long fin shubumkins, and alot of little Rosey minnows, and 2 Danio's. Those are 2 types of fish you can put in your aquarium that are happy with Goldfish, and the danio's and minows grow only to a few inches. My black moor, because they are so fancy with their tails and eyes they dont swim around much mine really a exciting day for him is he even swims 1/2 way up the tank lol he really just hoooovers the floor and sticks by the plants and rocks, he gets to much of a workout when he swims up top with the flowing water.

Just remember that all goldfish need, Water Conditioner, Filters, 65-75 degree water, the moor plants or decor you have the higher they should swim, also if you ad faster goldfish make sure ur black moor gets fed..my comets make it hard for mine to eat so i try to Individually feed him.

But ya get a 20-30gallon if you go to petco its 1g $1 so $20-$30 for a tank :D

you need a bigger tank eventually, and get another moor

he's depressed. how would you feel in his situation?