I predominately use FP4 as I feel comfortable with this film, however I have recently switched developers from ID-11 to Pyrocat-HD. As I develop 5x4 in BTZS tubes it was recommended to pre-soak the film in distilled water, partly to remove the AHL dyes and partly to ensure that the whole negative was wet before adding the developer.

My question stems then from trying Pyrocat-HD on 35mm FP4 which when soaked for the same time yeilds no dyes. So, does 35mm FP4 have AHL dyes like its 5x4 counterpart and if so doI need to worry about getting them out before 'pyroing'?
The negs are slightly different in colour between the sizes with the 5x4 being more 'brown'