Typically inorganic acids will be too strong in this use. These include the hydrochloric, sulfuric, etc. Acetic acid and citric acid are organic acids and tend to be "milder". They are also somewhat self buffering (Thomas pointed out the results of this).(posted 8813 days ago)Citric acid is used by many since it has a much milder odor. YOu could even use ascorbi acid (Vitamin C) but the cost is somewhat prohibative.