The best I have found that works is a solution called (VindEX). It's a spray bottle, before you put it on you MUST clean your indoor evaporator coil extremely well. After you clean your coil , cycle your fan on only until the coil is dry. Then use the entire bottle of vindex on your coil. And most importantly, you have to completely cover every inch of your coil. All copper, fin areas , U-bends, metal, everything.!! Once the bottle is empty turn the fan back on to dry coil. ... I have had over 100 cases of dss and vindex has worked on all of them.