brown marks are dirt, soap and conditioner that are lining the tank. this is due to low temperature washes witch do not fully disolve detergents. soda cristals on 60 dagrees should remove most of the deposits. 90 dagree wash (empty) with bio powder (not colour powder) every 2-3 months will help to stop the build up. don't change to liquid detergent as the build up is worse than powder.
skanxz
August 2007