Using Tetra AquaSafe in 1.5 gallon tank?

I have 6 glofish in the Tetra GloFish tank. It's getting so annoying buying distilled water week after week. I know there is a Tetra AquaSafe water conditioner... But on the back it has directions for a 10 gallon tank. I think it's one tablespoon per ten gallons. Is there anyway I can do this or divide that low and find something with that low of measure so my fish are not harmed?