Flux is a powerful query language used for time series data processing in InfluxDB, a popular open-source time series database. Intermediate Flux users may face challenges such as unawareness of common packages and utility functions, performance gains that can optimize queries, understanding when to use schema mutation functions, crafting tasks efficiently, and knowing when to write downsampling tasks. To overcome these hurdles, it's essential to learn about the available packages and utility functions, understand how to apply pushdown patterns for better query performance, know when to reserve schema mutation functions, utilize variables to improve task efficiency, and identify when downsampling tasks are necessary. By understanding these concepts and best practices, intermediate Flux users can optimize their queries, write more efficient tasks, and effectively manage their time series data in InfluxDB.