Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Anything acidic will help to remove the minerals, and vinegar, lemon juice or Cola are good. Do the washing away from the tank and rinse well.
It is better to do this more often, while the minerals are still soft. Not wait until they are rock hard and stuck on.
Test any product in a small area before using it on the main area of the cover. Or, if you have a scrap left over (DIY covers) then test the cleaning product on that scrap. Sure don't want to get rid of the mineral build up, just to be left with an all over cloudiness!