Tart Gin Cooler

I got off nice and early this evening and was craving a big glass of
something cold. This usually means a beer or soda but the cupboards
were bare. I located some tonic getting dusty in the back of a
cupboard then found this recipe. I like a gin and tonic ok, but this
is really good! The addition of bitters is nice. I put a pretty
healthy splash in. I think the Stirrings blood orange bitters would
work as well.

2 oz gin
2 oz pink grapefruit juice
2 oz tonic
Peychaud bitters (to taste)