Cap. Max concentration of hydrochloric acid you can buy is 38%, more than that won’t dissolve in water and just will bubble out. Sodium hydroxide isn’t good idea for neutralization either, because both are corrosive. Some carbonate like baking soda would be better. You can do better than that
Instead of that, some elbow grease and cleaning product with mild abrasive should do the job, and where that fails, for colorful (organic) stains bleach will work, and vinegar or up to 10% hydrochloric acid for limescale (white to orange, depending on how rusty your pipes are). Do not mix them together
Cap. Max concentration of hydrochloric acid you can buy is 38%, more than that won’t dissolve in water and just will bubble out. Sodium hydroxide isn’t good idea for neutralization either, because both are corrosive. Some carbonate like baking soda would be better. You can do better than that
Instead of that, some elbow grease and cleaning product with mild abrasive should do the job, and where that fails, for colorful (organic) stains bleach will work, and vinegar or up to 10% hydrochloric acid for limescale (white to orange, depending on how rusty your pipes are). Do not mix them together