I've been consuming electrolytes before and after sports disolved into water without sugar.
Can electrolytes in high volume make you gain weight?
You are drinking flavored salt water. If it has no calories it can't make you fat but it can make you feel bloated.
Mayo clinic references too much sodium can lead to water retention. So maybe in the short term it could make you retain a percent of an ounce of water in your system. Not fat but maybe feeling fat and maybe weighing (slightly) more on a scale the next day.