Hi Guys
It's worth taking this back to basics.
We either oxidise, hydrogen peroxide, sodium hypochlorite(household bleach, too strong for most apps) or reduce, sodium met, oxalic acid.
Oxidisers are accelerated by alkali, hence ammonia added and reducers acid, therefore citric acid.
If you have all the ingredients you can mix yourselves a fresh solution and apply hot.
Cheers
Doug