guppies should be kept 1 male to every 3 females or all males. Otherwise the males shorten them life spans of the females.
if its a male guppy. They do bend their backs as part of a mating display.
Guppies are normally found in hard water in most of their native range. A tablespoon of aquarium salt per gallon may help with raising the alk and ph and provide some balancing effect.
But i would do after a water change, how big is the tank?