If you've ever noticed white, chalky spots on your car's paint after washing it, you're not alone. These spots are caused by hard water, which contains minerals like calcium and magnesium that can leave behind unsightly marks. Fortunately, there's a simple solution: wheel acid.

Before you get started, make sure your car is wet and out of direct sunlight. Wheel acid is a strong chemical and should be used with caution. It's best to work panel by panel to ensure that the acid doesn't sit on the paint for too long.

Here's how to use wheel acid to remove hard water marks from your car:

1. Wet the panel: Start by thoroughly wetting the panel you're going to work on. This will help to prevent the acid from drying out too quickly and damaging the paint.

2. Apply the acid: Spray the wheel acid onto the panel, making sure to cover it completely. Avoid getting the acid on any areas that aren't affected by hard water marks.

3. Wash it in: Use a wash mitt, such as the Autofiber Monster wash mitt, to gently wash the acid into the paint. Be careful not to scrub too hard, as this could damage the paint. Work in small sections, rinsing the mitt frequently to avoid spreading the hard water marks around.

4. Hose it off: Once you've washed in the acid, rinse the panel thoroughly with water. Make sure you remove all traces of the acid to prevent it from causing damage to your paint.

5. Repeat if necessary: If the hard water marks are particularly stubborn, you may need to repeat the process a few times. Just be sure to work slowly and carefully to avoid damaging the paint.

Remember, wheel acid is a strong chemical and should be used with caution. Always wear gloves and eye protection, and avoid getting the acid on any areas of your car that aren't affected by hard water marks. With a little care and attention, you can use wheel acid to remove hard water marks and restore your car's paint to its former glory.