Scum Lines are frowned upon in the boating realm!
Here are 3 pointers on how to keep your Waterline clean!
Use On/Off by Mary Kate to get your Waterline clean.
It is very acidic so be very careful not to get it on your skin or inhale it. Use a scrub brush to brush it onto the stained area. Hose off when the yellow has gone away
Apply a Wax
Keep a coat of wax on the waterline. It will help repel the scum line. Meguiars Premium Wax or Collinite #925 are both good choices and last a long time.
Washing the waterline regularly will help keep the waterline off and minimize the amount of On/Off you use. If you let it sit for too long, you will have to use the acidic cleaner.
Maintenance is key when trying to keep your Waterline clean! Buy some On/Off from West Marine, a good wax, and a brush in order to keep your waterline clean!