Powder Residue Left On Dark Clothes

Hello Sparky. Here are the most likely causes of your whitish marks on your washing -

White streaks of fine powder are usually caused by overloading. If you rewash the affected garments without any detergent the marks should come out if that's what they are. If there is too much washing inside the drum then it turns round in one mass and the laundry doesn't get chance to open up. Undissolved detergent can get trapped inside folds in particular

If you place the detergent in a container inside the drum then make sure it's placed right on top of all the laundry and preferably towards the back of the washing machine drum to prevent it getting trapped under parts of the laundry and restricting the dispersion of detergent

If you don't use the proper amount, some powdered detergents, can react with minerals in hard water causing a whitish residue that looks similar to undissolved detergent. Make sure you use the right dosage according to the type of water in your area and the soiling level

Low cold water pressure (or even a partially kinked fill hose) can mean that if detergent is placed in the soap dispenser drawer it may not be flushed efficiently into the drum on wash. This can leave some detergent inside the soap dispenser drawer or even underneath the drawer in the bottom of the dispenser. This detergent then gets flushed onto the laundry during rinsing

White streaks or residual washing powder after washing (my white goods Blog)