Hi, make sure you wash your retainers immediately after removing them. Washing them later before reinserting in your mouth can lead to hardening of debris already accumulated on your retainer surfaces. It’s better to brush out your retainer after every meal and also brush your teeth at the same time. For a deeper cleansing, you can mix lukewarm water with a dish soap ( avoid toothpaste as they contain abrasives which can scratch the retainer surface) you can use a soft toothbrush to gently scrub away the debris.

Brush your retainers with Clinsodent tooth paste or ask your dental surgeon for proper maintenance of aligners

U can use a soft brush to clean the retainer

Often such a such situations occurs with clear aligners. Get your teeth cleaned professionally at regular intervals. Also the retianer can be cleaned using a tooth brush with extra soft bristles and gel based paste , very gently and washed under tap water. Avoid using any abrasives.