Best chemical for removing waterline green mark

I have heard of this but wondered if getting dried on wallpaper paste off was an issue. So I just use oxalic acid in hot water, the heat really helps it work,

I overdid the wallpaper paste thickness with oxalic acid one year and found it ended up as very fine crystals which were difficult to shift with cold water from the hose. If you haven't used oxalic before as Mikebz says - it's rubbish when cold, magic when air/surfaces warm.
 
Yes, an acid cleaner.

Remember that the acid will do a number on the bottom paint.

Personally, for that I would wear dark glasses or stand farther away. It's a boat, not a chandelier. It will come back anyway, so bugger.
 
surprised to see this thread back to life..
in the end Harpick 10 in one (in a black bottle) did a fantastic job on the waterline and also on the teak rubbing strake and other woodwork.
 
Nip down the chandlery and get a bottle of Starbrite Hull Cleaner £19.95 ... dead easy to use, works a treat and costs peanuts! .. Eh? .. How much did your boat cost? ... :encouragement:
 
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