I don't use caustic unless I really have too like stripping old sealers of course. Like Ralph said caustic/stripper is very tough on wood. I've never used a pre carb cleaner cause the 12% mix has always worked for me. If 12% is mixed at the right strength not to strong it can be very effective without causing damage. I've started adding the caustic to my mix in the last few years and has worked great as a boosted up mix. I like a 12% mix when lots of mildew
If this is a yest fence for you try different methods and see how they work yourself in person. You can make a 12%/water/soap mix and try adding caustic. Depending how strong your 12% is you might need a 50/50 mix without caustic.
This deck for as bad as it looked was cleaned with that same 12%/caustic mix I gave you then brightened.