Note: prices jump around, so compare these various vendors ' current prices - prices listed here are current as of June 2018.
1 lb bag of oxalic acid $10 + free shipping ($9/lb)
2 lb bag of oxalic acid $12 + free shipping ($6/lb)
5 lb bag of oxalic acid BEST DEAL! $15 and FREE shipping ($3/lb)
Star brite Instant Hull Cleaner gets rave reviews. FIVE STARS! It should because it's 5--10% oxalic acid! You can read the exact ingredients of Star Brite Hull Cleaner here.
Last time I looked it was $20 for 32 ounces (a quart) of Star Brite. And free shipping with Amazon Prime. Let me do the math…let's say it 8% oxalic acid because they say it's between 5 and 10 percent. 8% of 32 ounces is 2.56 ounces of oxalic acid. I'll be generous and say the oxalic acid is $5 a pound (although you can get it for around $3/pound).
$5/16 oz = $ .32 (32 cents an ounce)
$ .32 x 2.56 oz = $ .82 (82 cents)
Star Brite is good stuff and it will work for you, but you are paying over $16 for them to mix it up and put it in a bottle for you. You can make a quart for under a dollar.
I looked up a store-bought hull cleaner's MSDS (material safety data sheet which lists ingredients) and lo and behold...it is 1 to 5 percent 2-Butoxyethanol (a degreaser, like a soap) and 5 to 10 percent oxalic acid! Let's say it is 8% oxalic acid…that's about 2.5 ounces per quart. At $16 a quart on Amazon, you're paying about $102.40 a pound for the oxalic acid.
So pre-mixed is about $16 a quart. If you mix up your own it's about fifty cents to make a quart!!
The recipe is simple, but remember, oxalic acid is 3,000 times more acidic than vinegar, so wear gloves and goggles. And don't breath it for gosh sakes! Doing this outdoors is a good idea.
Put 1 quart of hot tap water in a container (a bucket, for instance).
Measure 100 grams (about 4 ounces) of oxalic acid.
Stir the oxalic acid into the hot water.
Let the mixture cool and it's ready to use.
Optional: if you want it to "stick" better to a surface, you can add up to 10 tablespoons of powdered wallpaper paste.
Note: some store brands use only 1.5 ounces of oxalic acid per quart of water and many people say they work, too.
First off, wear latex or nitrile gloves and goggles when using oxalic acid. And don’t breath the straight powder!
Applying it is simple. At first we wiped it on with a rag.
Later we used a gallon pump sprayer, sprayed it on and let it sit for a few minutes. Then we went back and hosed it off with lots of water.
Don't leave it on metal for long. It can remove rust, but also zinc from brass.
For really thick algae growth, I scraped the hull with a plastic scraper (I even used a plastic ruler sometimes).
You may want to apply a good wax or other coating after cleaning.
(long version 14 minutes) The first couple minutes show how to mix it up, and the rest of the video shows how well it works
Full disclosure: I have personally bought and used almost everything I mention on my web site. I search for good deals on good products for myself and tell you where to find them. If you buy from Amazon I do get a small commission, but you get the same price you would anyway. Most of the other stores I mention pay me nothing, but if they are convenient or have a good deal, I tell you.
Thanks for your support. I'm not getting rich doing this. When folks use the product links I can see they care. It is a fair amount of work keeping the site up. And of course you can email me anytime.