What is the name of this mermaid movie?

I've been trying to remember the name of this mermaid movie I watched when I was a kid and can't for the life of me. It was about this girl who took a cream from her parents office (they were scientists). The cream was supposed to make one a better swimmer. So she goes to a pool party and uses the cream before swimming. Another girl sees her and uses it when no one can see her. They both turn into mermaids and eventually end up kidnapped and exhibitioned in an aquarium. Then the family of the girl whose parents made the cream have to go rescue the two girls from the aquarium. I also remember the girls were chilling in a hot tub when they were kidnapped. Can anyone recall the name of this movie? It's been driving me nuts that I can't remember the name when I remember the whole film. Thanks!