For general cleanups try sugarsoap. Its cheap and works well on ingrained gunge and strange things growing in treadmaster-especially if you scrub it with a stiff brush.
Oxalic Acid can be used to remove stains from GRP and is also an excellent treatment for teak. If your decks are teak, however, you should NEVER EVER use a power washer on them. Sponge, or in extremis, a softish brush, is the most that should be used.
<hr width=100% size=1><font color=blue>A convert to steel boats and displacement cruising - the only way to go</font color=blue>
I've heard that Oxalic acid used regularly ( once every 2 or 3 seasons) starts to make the gel coat slight porous which leads to it getting the brown staining worse and more quickly - any comments?
I used to use it once per season, at winter lift-out time, to remove those brown water-line stains that seem resistant to just about everything else. Never had any problems, didn't even dull my painted boot-top line. But perhaps it wouldn't pay to leave it on 'to soak', it is an acid after all. So wipe it on, give it a rub, wipe it off and wash down with clean water. Good luck.
<hr width=100% size=1><font color=blue>A convert to steel boats and displacement cruising - the only way to go</font color=blue>