Is it possible to decrypt external hard drive without losing data? I have a USB 3 external hard drive that I use for video media, it's HFS Journaled Encrypted. I have about 1 TB of data on it, but I no longer need it encrypted because I need the faster speed. 

Is is possible to remove the encryption on the drive while still retaining all the data?
Yes it is possible to decrypt a disk. This option is directly accessible from the Finder popup menu.
Simply make a ⌃ ctrlclic on the disk icon on the Desktop:

and select the entry starting with Decrypt…. Then enter the encryption key (or password as you prefer to name it) and confirm.
This function will of course take care of conserving all the data by performing it step by step (because you never have half of a disk free to use for this operation).
Take care the alimentation and the connection cable to your disk are
protected against any break during this operation which may take a few hours.