Hello, brand new to the forum. I have just started an aquarium and am in a bit of a pickle. I dont know if its 15 or 20 gallons. Its an old Hex tank my mother had. Each panel is 9"w x 18"h. I think its 15 gallons but didn't know if someone was better at math then I. Next question! I got gravel fake plants and a nice center piece with a bubble in it.....WHAT NEXT!? I dropped in one of those cycling tablets. What fish would be suited to live together? I just like colorful, interesting fish, but will most likely just buying from PetSmart so my choices arn't that grand. I know I sound dumb but I just want to do this right!