In slow cooker, place both cereals. Add pretzels, fish crackers, and almonds.
In small bowl, stir together butter and seasoning mix with whisk until well combined. Pour over cereal mixture; stir until evenly coated.
Cook uncovered on High* heat setting 2 hours, stirring every 15 to 20 minutes.
Spread mixture on cookie sheet or tray; cool 3 to 5 minutes before serving.
*Different slow cookers have different amounts of power. If your slow cooker runs hot, you should probably start on "Low" temperature to make sure that the mix doesn't burn. Plus, keep a close eye on it and make sure that you're stirring regularly.