Quick check before work. Rust on steerer tube was just sitting on surface. A VERY light brush with a small wire brush lifted the rust off. Not sure if the paint around the crown race is lifting, will take out later and dry to see if any of the paint has been affected.
The next step is to put one more cup so it equals 1 cup per 5litres of water and drop something rusty in and see if that would work quicker without paint coming off, maybe turn the fork around?

Before light brush

After light brush.