Remove stubborn toilet stains: How to use muriatic acid the expert way

Yes, keeping your toilet unstained often seems like an insurmountable task -- but there has to be a better, more affordable option than ripping it out and starting all over again, right? (Staten Island Advance photos)

STATEN ISLAND, N.Y. -- OK, some might argue that there are only two things a human truly must do: Die and pay taxes.

False! They left one crucial necessity outta the loop. We all gotta go to the bathroom, baby. And with nature's calling comes another unavoidable truth: Toilet stains.

How do you get rid of these stubborn things?

That's a timeless question for Tim Carter, the always handy mastermind behind

Q. I'm at my wits' end with toilet bowl cleaners. My toilet has light and dark stains in the bottom of the bowl, as well as up under the rim. I've tried the usual brands of toilet bowl cleaner, and none of them does anything to cut the stains. What's causing the stains? And what, if anything, can I do to get my toilet looking respectable? It's embarrassing, and I'm about ready to rip out the toilet and buy a new one. Help me please.A. I know where you're coming from. I remember years ago trying to restore a deeply stained toilet in the basement of a past house I owned. I have clear memories of wearing rubber gloves and goggles as I tried all the different cleaning products at the grocery store as well as every type of brush and scrubbing pad known to man.

Photo/Tim CarterThe typical toilet bowl cleaners you get at the grocery store often don't have the power to rid a toilet of stains caused by hard water mineral deposits.

The good news is that I eventually succeeded, but only after I stepped back and thought about some of the things I had learned in my college chemistry and geology lab classes.

Based upon your description of the stains and your inability to make progress using ordinary cleaning products, I'm convinced you're a victim of hard water and lime buildup. It's very common in many areas of the U.S., especially where there are minerals in the water supply.


Remove stubborn toilet stains: How to use muriatic acid the expert way

If you have calcium, magnesium and a few other elements in your water, these can create multilayered deposits inside a toilet. Not only can these deposits be unsightly, but they can also undercut the performance of the toilet. If your toilet is like several I've had, you've also noticed that the flushing has become sluggish or not as powerful as it once was.

The ugly stains appear when dirt gets trapped in between layers of hard water deposits in the toilet. This is most common under the rim and along the sides of the toilet bowl above the water line. Each time you flush, these areas of the toilet get wet. When the water evaporates, it leaves behind an ultra-thin film of minerals. Dirt can easily attach itself to this coarse film. Then the next flush and mineral buildup locks in the stain. After thousands of flushes, you can have quite an ugly stain.

You can also get a lime layer buildup in the bottom of the toilet bowl that starts to block the siphon jet hole. It's very important that this hole is wide open so that the maximum amount of water can enter the toilet bowl as fast as possible to initiate the flush. Water entering through the rim of the bowl can also be slowed by mineral deposits in the small holes under the rim.

The best toilet bowl cleaner I've come across in these situations is muriatic acid. This is a very powerful chemical that should be used with great care and respect. The fumes are very nasty, and the acid can easily cause skin burns and ruin fabrics that it soaks into. However, when this acid contacts lime and other hard-water deposits, it rapidly dissolves them. Once the deposits have been removed, the toilet looks brand new.

I always start the cleaning project by using the standard toilet bowl cleaners to sanitize the bowl. Once this is complete, I rapidly pour 5 gallons of water into the bowl to simulate a flush. This leaves a small amount of water in the bottom of the bowl. Then I slowly pour about 12 ounces of muriatic acid into the bowl.

Be sure you have the bathroom well ventilated, preferably with a window open to exhaust the acid fumes. Wear tight-fitting goggles, rubber gloves, old clothes with long sleeves, etc. so that you have virtually no skin exposed. Carefully use a toilet brush to spread the acid solution under the rim of the bowl. Do this multiple times over a period of 30 minutes.

Let the acid solution work for up to an hour or two. If you have to leave the room always put the toilet lid down to prevent animals from getting into the acid solution. If children are in the house, never leave the toilet alone. Work until the job is finished.


The muriatic acid will absolutely remove the hard water deposits that are trapping the stains. The longer it soaks, the less you have to scrub. Never use a metal scraper, screwdriver or other tool to dislodge any deposits. The acid will do the work for you; it just may take awhile.

Avoid using any abrasive toilet bowl cleaners. These can scratch the smooth glazed surface of the china. If you take your time and slosh the acid around the bowl and twist the brush in all visible areas, the stains and deposits will disappear. Flush the toilet several times when you think you're finished. Repeat the process if there are stubborn stains that didn't come clean the first time using the industrial-strength toilet bowl cleaner.

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