This is a episode of The SpongeBob Chronicles.
Plot
A new drink has arrived called Kelpsi, and Mr. Krabs thinks something's fishy with it. He goes to Kelpsi HQ, demanding the recipe for Kelpsi. The president says the recipe has nothing that's mysterious or bad. Mr. Krabs comes back, angry, saying he knows there's something wrong. SpongeBob starts drinking it. A day later, he loves it. Mr. Krabs knows there's REALLY something wrong here. Months later, the whole company shuts down because of health failures. Mr. Krabs just smiles...