why dont you believe in melafix?Dont know how long you had this chromis, but it seems like common symptoms observed from fish recently unpacked from transhipping.
Never medicate main tank with any med especially with LR/Inverts.
I personally dont have much faith on Mela/Pima on f/w, definitely none for s/w.
If decided to treat main tank, Should shutoff skimmer and remove L/R and Inverts until treatment is completed and main tank water is well skimmed and/or chemically adsorbing resins are used along with necessary pwc after the treatment in order to remove any remaining residues from treatment.
Before buying any fish, always ask how long they had the fish in store. Especially s/w fish due to how they are packed and shipped and new fish should be given ample to adjust to new enivornment (water and & captivity) before selling to public but unfortunately such procedures usually are not followed by lfs. Thus ask before spending money.
One can ask lfs to feed "tiny" amount of food in which you can determine alertness of fish. Make sure it is tiny bit as they can throw up all the food while being chased to be bagged or in the bag on the way home, which also can pose threat to health of new fish.
Good Luck with new Fish whichever you choose to go with.