I have a bathroom shower drain that is backing up when I flush my commode, can you put acid in the drain, the house was built in 1963 and I have had some plumbing change out done it is a combination of PVC and Cast Iron.. Thanks!

I have a bathroom shower drain that is backing up when I flush my commode, can you put acid in the drain, the house was built in 1963 and I have had some plumbing change out done it is a combination of PVC and Cast Iron...? Thanks!
FORGET THE ACID!!
Snake from the lavatory roof vent or the shower drain.
I can not advise against using muratic acid, or any acid, in a enclosed area such as a rest room strongly enough. As a young boy I would take limed up toilet bowls out in the alley behind the shop and boil the lime out of them. Over half a century later my lungs still carry the scar tissue that the acid fumes caused. A few years ago I lost a good friend when he used a commercial drain cleaner containing sulfuric acid in a unvented bathroom. Acid IS NOT A GOOD IDEA to use to clear mineral buildup. Take it from one who's paid the price. Regards, Tom