fish in perpendicular stand

Question
Over the last week one of my guppies has begun to slowly swim and rest with its body perpendicular... tail to the bottom of the tank, head to the top.  There is no ick or any disease looking spots on it.  What is wrong with the fish?

Answer
Lee,                                                         Medicate your tank immediately with tetracycline. They have swim bladder infections. This is  broad spectrum antiobiotic and they have a bacterial infection. Treat and remove your carbon from your filter. After 7 days of treatment do a 25 % water change and new carbon. Everyone should be ok if you do this now,also after, add aquarium salt...cheap , 1 tablespoon per 5 gallons.It will help with stress and help them rid their bodies of wastes.Just remember it is a mineral and does not evaporate so only add when you do water changes...... adjust amount for the amount siphoned out. Good Luck, Tina