what concentration HCL on gelcoat to remove tannin from mangroves

[FortMyersFisher]

I boat in mangrove lined backwater. The mangroves release tannin (same stuff as in red wine), that leave a yellow / brown stain on your hull that won't come off with regular boat cleaners. I want to get this off and everyone says acid. (different people have their different favorite acid). I'm going to use HCL / hydrochloric / muriatic, because I have used it before for other applications. I have all the safety equipment. My question is, what concentration? There are big differences between 5%, 10%, 25%, 100% (forget that), etc.

[keith001]

Muritic acid comes at 35%. I dilute it 6:1, which is still strong. Works well with a little brushing.

[slug]

I don’t use any HCL on boat..it badly stains stainless steel

To remove the brown mustache and for general decal, organic stain removal , metal cleaning use oxalic acid or phosphoric

Sulfamic acid is another handy acid product for onboard use..de scaling

What concentration ..hmm unknown...start mild,

Let the acid stand and work a while

Stain still present ..repeat

Don’t work in bright sun

[captd44]

Go to the dollar store and get toilet bowl cleaner and brush on and rinse off. A good wax can help prevent this.

[WSMFP]

Originally Posted by captd44

Go to the dollar store and get toilet bowl cleaner and brush on and rinse off. A good wax can help prevent this.

This. "The Works" toliet bowl cleaner from dollar general works great.

[Captain Bill]

I use phosphoric acid. I use about a quart in a 2 gallon garden sprayer and dilute with water. It's enough to clean the bottom of my 44 catamaran with some spare. Mist it on and walk away for an hour and then rinse it off. Like all acid washes it will change the color of bottom paints, so I usually do this before I bottom paint. HCL is a gas dissolved in water and comes out of solution rather easily and is a bit hard on the lungs. Phosphoric acid is not a gas so does not have this problem. Oxalic is probably similar but I've found it takes a bit of scrubbing.

[cabo_sailor]

Haven’t tried it personally but some people use lemons. Cut in half and use each half as scrub pad.

[GordMay]

Greetings and welcome aboard the CF, Fisher.

Originally Posted by slug

... To remove the brown mustache and for general decal, organic stain removal , metal cleaning use oxalic acid or phosphoric ...

Indeed.