Another thing to add is the active and fast paced swimming of comets aren't compatible with the pudgy goldfish.
If you're going to keep only these 2 pudgy guys, I would do the MIN 40 gallons.(20 gallons for the 1st adult/10 gallons for every adult after the 1st) But it is always best to go bigger for these guys. They are high waste producers and as such, a larger tank/filtration will help maintain the waste they produce.
However, being that one of them is a comet and not one of the pudgy goldies. You will need a much larger tank like Kio mentioned. Based off the different swimming patterns that are NOT compatible, I definitely would rehome the comet. If you truly love your comet, you would do what it best for her and not be selfish by continuing to keep her in a home that is too small for her.
Last edited by FishyFishy89; 10-09-2013 at 03:12 PM..