Both are rubbish as ph down, ph down needs to be stable, citric acid will rise back up to the initial ph of the tap water in a matter of hours
@benn0 knows how useless it is.
Normally I would recommend phosphoric acid, a very stable, relatively safe acid which is generally the form of acid used in bottled PH down.
The general consensus regarding living soil is that ph down is not needed as the microbial life breaks down organic ferts to feed the plants.
From what I gathered lowering ph isn't needed for soil.
But since you're asking (and since you made it clear that you're more keen on organics vs synthetics) you can lower it by using
Organic gypsum (calcium sulphate) which will help buffer the soil to be slightly acidic.
Humic and fulvic acid will also be ideal, gogo juice and Searles 5 in 1 organic brings ph down to around 6.0-6.5 for myself, loaded with humuc/fulvic
Chicken manure will act as a neutral buffer too around 6.5 - 7..
If you've got alkaline water from the tap then I'd just mix gypsum in to your soil mix.
perhaps
@itchybro has some good advice