I have my own rat and my friends rat in the same tank but I think that its not big enough for both of them. I don't know what to do... Wait until I have enough money for a bigger tank (could take a couple months) or should I get rid of my friend's rat? They've been together since they left the litter, so I don't know if its a big deal... I'd say they're about 1/2 the size of a full grown rat.
How big is the tank these rats are in? Fish tanks aren't the greatest thing you can house rats in The ventilation is crap and there's nothing for the rats to climb up. The best thing(In my opinion) to house them in is bird cages. See if you can get a large cage suitable for a cockatiel and fit it out with a fleecy hammock toys and a wheel(If the rats use one) and the various food and water bowls they use. I have 26 rats at the moment and have made most of their cages out of those large plastic roller boxes you can get at hardware and discount variety shops. I heat up a knife and cut the sides out and replace them with aviary wire held in place with garden twine/sandwich bag ties. This method of housing is cheap and easy to move/clean. I hope this helps you. I wouldn't get rid of your friends rat. Rats are much happier if they have their own kind fro company. PM me if you want/need any more help in regard to housing or general rat care. Cheers!
My rat is in a 5 foot high, 2 foot wide kitty condo dubbed Chateau Du Ben. He climbs all over this thing like no one's business.