Removing algae stains

I went to the garage to take out my kayak and noticed that I have algae stains on my kayak. Tried to clean it off with 409, Fantastic, Soft Scrub…all to no avail. The boat always has a nice shine due to the 303 I use on it, but the algae stains are a bit unsightly. The stains are along the waterline and I usually just have to rinse the algae off before I take the boat out of the lake. I probably didn’t clean the boat after the last paddle last year. Any suggestions.

Poly boat, or composite?
Poly is fairly impervious to many solvents. Composite may be susceptible to acetone to a certain extent.

Is it algae or mildew?
And how are you storing your boat? Covered with a tarp? Garage?


QCC composite
The kayak is a QCC composite fiberglass over kevlar.

The stain is algae not mildew. The boat is stored inside in a dry, airy garage. I paddle on lakes and ponds in CT and collect algae at the waterline starting about July. I usually rinse it off before taking the boat out of the water every time or right after I get home. It appears that I left some residue on the boat after the last paddle of the season last October. It’s not a dark stain, more of a shadow at the waterline, but I see it and would like to clean it off.

Thanks for your help.

If it were my boat
I would try applying a little acetone to a small area to assess the result. I have used acetone to remove stains or oxidation from many Royalex or gelcoated composite boats without ill effect.

Obviously, acetone can potentially cause major damage on prolonged contact, but it evaporates very quickly when a cloth is moistened with it, and used lightly on the hull.

I do wash the hull with soap and water after application. Thus far, I have not had problems with the solvent dulling the gelcoat.

Magic Eraser
Try one of these new sponges that you can get at most grocery or department stores like the MR. Clean Magic Eraser.

You will be surprised at what these things will remove. Not a clue on how they work, but on many problematic stains I have found them quite effective.

If it works on algae as well let us know.

kind of interesting
I noticed the same thing on my QCC 700x this spring when it came out of the garage.

Good cleaner and polish combo

– Last Updated: Apr-25-09 12:53 PM EST –

Try the acetone as already mentioned, but I tend t reserve that for small spots.

A good marine cleaner/boat wash made for hulls would be a good start. These are usually boi/env friendly - and so use enzymes vs chemicals - and tend to be very good on waterline stains.

From there, what is left should go away with a decent marine polish. I like Starbrite marine polish for this as it is great on gelcoat and any dirt that I though was a permanent stain after washing alway seems to disappear as I apply it.

Point here is the marine products are better for this and worth any extra cost. I only do this every year or two as keeping it pretty is not a priority, but it's quick and easy and I am always pleased with the result.

Bonus here is that the polish then also prevents a lot of gunk from sticking/building up - for a while anyway. I used to rinse off the bath tub ring after every padle, now I rarely do.