You can add a little lemon juice also. Liquid Shield works great, see Usage Guide , page 3. Liquid Shield works very well, see Usage Guide page 4. Avoid all fragrance, dye, chlorine, ammonia, optical brighteners. You can mix baking soda others.
Some folk use the laundry disks.
One reader suggests Biopac or Global Balance products. Also you can get pumice stone to get the mineral ring out of porcelain toilets and sinks. Cedar, bay leaf, and clove help, but are allergenic to many people. Because each person can react differently, no product can be guaranteed safe for everyone. Commercial 'hypoallergenic' brands cause problems for many people.