In response to falling sales of diet soda, last year PepsiCo changed the sweetener in its main calorie-free beverage, Diet Pepsi. Noting the health concerns that some customers have about the original sweetener in Diet Pepsi, aspartame, the company switched to a different sweetener last year to try to reverse a sales decline. Now sales are declining even faster.

Customers had time to adjust to the idea of Diet Pepsi without aspartame, since rumors about sweetener tests have appeared in these very pages since 2012.

The version of the beverage sweetened with a blend of sucralose (Splenda) and acesulfame potassium (branded as “Ace K”) started to appear on shelves last summer, just in time for peak cold-beverage season, and the company admitted that some fans of the beverage were not happy with the new formula. Specifically, they received about 3,000 complaints from customers, and only about 300 compliments for the new formula.

The Wall Street Journal reports that some local Pepsi bottlers have received notice that changes will be coming to the brand’s diet sodas soon. Pepsi declined to comment on the matter.

The problem seems to be that the brand’s existing fans don’t like the new formula, and the company didn’t pick up any new fans or health halo benefits by switching to the new sweetener blend.

While diet soda sales in general fell about 6.7% from February to May, according to Nielsen data cited by the Wall Street Journal, sales of Diet Pepsi are down 12%. One beverage industry consultant suggested that maybe Pepsi should change the brand name as well as the sweetener. Maybe the whole idea of “diet” sodas has run its course.

PepsiCo Weighs Another Fix to Diet Pepsi [Wall Street Journal]

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