I had need to remove a radiator for decorating and decided to top up
the system with a corrosion inhibitor when I replaced the radiator and
refilled. The header tank was liberally coated on the sides and
bottom with a thick brown slime, likely some organic growth I guess.
Is growth in these tanks normal and how often should they be cleaned?
I would guess this tank has not been looked at for the past ten years
or so as is likely common with most tanks.