I've used arnica since QVC began and adore it! you can buy it as a gel and as a bath soak. SBC make one that has a high concentration of pure Arnica. Others dilute it.
Bath soak :-
You only need one pump in the bath [don't be rude!] the bath soak is also good to add to a bowl of hot as you can stand water for hands lower arms and feet. A bonus is that if u soak a towel in it, you can put in on parts that won't fit in a bowl ! use a binbag or open out a carrier bag and place over the towel, then put a dry towel over the top to keep the heat in - bliss! of coarse it's less messy if :-
a] someone can wring most of the water out;
b] don't add too much water in the 1st place;
c] can wrap the towel around a joint then put into the carrier.
Bonus - you can still soak other bits in bowl at same time!
I used to have a carer assisted bath and always added the bath soak. After a different carer had been, the next day the agency rang to ask what was in the water - thinking oh no "where there's blame, etc... she eplaind that the carerwanted to buy it immediately. apparently she'd slept well for the first time in months after breaking her wrist. How's that for a blind test!
Gel :- [not on open/broken skin]
put just a little on your fingers and gently
pat onto tender achy bits , don't rub or pre-warm.