A very safe concentrated Citric Cleaner is TKO Orange Concentrate or it may be called Orange TKO concentrate. Locate the home page and do some reading on it.
I put a full 16 oz. bottle of it in a half full bath tub of Hot water. Too soak and clean some older 1950's horns. Gave them a good long soak. Help a lot in the cleaning and took off every bit of the old Cellouse laquer. Could wipe it off with a wash cloth and hand. Turned the laquer to gum. Caused no harm to me or the brass/silver of horn/valves etc..
I still use it today in less strength, along with Simple Green/Dawn degreaser. With good hot water soak,does a great cleaning job. Sanitizes and gives horns a nice smell. Causes no problems with plated metal or all brass horns. To strong of a strength may remove new laquer though.
My wife uses this TKO Orange product to clean our Fish's fish bowl once a month. Never harmed the Fish. I am a Asthmatic,the TKO or Simple Green have never bothered my breathing. This stuff is about Citric Acid as you can buy. Good luck