Swimming Pool Blog

Help! My pool is stained!

by Rob Cox, May 18, 2010

Swimming Pool Stains ~ Identification & Removal

stained pool

Stains on the pool! Nobody likes to look at a stained pool, and even fewer want to swim in a stained swimming pool! Pool stains can form from neglect or from poor source water. Plastered pools are more susceptible to stains than vinyl lined pools or fiberglass pools, so the focus of this article will be on identifying and removing stains from a plaster pool.

If you have a stained vinyl pool or fiberglass pool stains, the techniques described here may not apply. I have planned follow-up articles on how to identify and remove stains from a vinyl liner pool and how to remove stains from a fiberglass swimming pool. 

What if I have well-water?  Well water is infamous for staining pools with high levels of iron, manganese and other heavy metals that can deposit themselves on the pool surface. If you fill your pool from a well, you would be "well-advised" to use a sequestering agent upon initial fill, followed by regular maintenance doses. Sequestering agents, also called Chelators, do their best to keep minerals tied-up (sequestered, like the OJ jurors) in solution, so that they don't precipitate out of solution and stain your pool surfaces.

Sequestering agents are sold under many brand names, usually with names like "Stain & Scale" or "Metal Magnet". They do not remove stains, but used properly, may prevent some mineral stains from occurring. Many brands abound, I like the GLB Super Sequa-Sol product.




Plaster, grout, mortar, cal-hypo chlorine shock

white crystals or precipitate


Fiberglass Shells

red, blue, gray, or black


Copper algaecides, ionizers, corrosion of copper pipes, fittings and heaters

blue, green, teal, black


Well water, corrosion of iron pipe and fittings

dark, red, brown, black, gray


Well water

pink, red, black or red

This Chart is from our Pool Stains info page. Check it for more information on the sources of pool stains.


Pool Stain Removal:

1. Drain and Acid Wash the plaster pool. This is the most radical treatment, and it is a purposeful stripping of the top 1/16" of the plaster surface. Not something that is without risk, and not something that you can do every year - eventually you'll run out of plaster to strip! The risk comes from empty pools, dangerous chemicals, and possible enviromental problems from the acid, unless you balance the waste water before pumping out. I would recommend that acid washing a pool be done by a professional. See our pool acid wash page for more information on this procedure.

2. Use the No-Dran Acid Wash Kit. This kit and instructions allow you to get close to the same effect of an no dran acid washacid washing, without all of the hazards. You don't empty the pool, but follow the instructions to bring the pool water level down to a very low pH level. Acids combined with some sort of  "Jocks Magic" (sorry, couldn't resist poking fun at the product's creator Jock Hamilton), result in a fresh finish for dull, stained plastered pools. This is a popular item in areas that cannot drain the pool due to a low water table, which can create the risk of "floating" or "popping" the pool if drained. Also popular for those pools out in the country, off of the city water line. Filling from a small well sometimes takes too long, and trucked in water can be very expensive.

3. Use Ascorbic Acid - Linus Pauling would approve! Regular Vitamin C, Ascorbic Acid, can in some cases remove stains on a plaster pool. This product can be expensive, but imagine how healthy the water is to swim in! Just kidding, using Ascorbic Acid in your pool water has not been shown to make healthier swimmers! If you have some Vitamin C tablets, crush up a small handful to a coarse powder. Sprinkle the crushed Vitamin C tablets over the stain. If the stain is removed by this test, this may be the treatment of choice for your particular stain. We have containers of Ascorbic Acid for pool stains.

4. Use a Stain Master - The Jandy StainMaster is a device you connect to your pool pole. It has a small diameter, 25 ft hose with a gallon jug cap on the other end. Connect the cap to a gallon of muriatic acid, prime the hose, and you can deliver stain fighting muriatic acid directly to the source of stains. Very effective at plaster pool spot removal, but slow for large stained areas. I once made a "Turbo StainMaster" out of a frisbee, and an enlarged hose. I should of taken a picture of it! We have the regular Jandy Stain Master available.

5. Use Jack's Magic Products. You gotta hand it to Jack. Developing a complete system for pool stain identification and removal. The product line has now expanded to include water treatment chemicals, algaecides and other "stuff", but the main focus is pool stain removal  Jack's a bit cheeky, using the naming convention of calling everything by it's color or purpose + "Stuff". Blue Stuff, Sapphire Stuff, Step Stuff , etc. Jack's Magic products have been around now for 10-15 years, so it seems to be working out and catching on. My experience has been that they usually work, but you must follow directions explicitly, and don't cry if it doesn't work. Try something else.

6. Use Pool Stain Treat. Jock Hamilton is at it again. This is probably the most successful products from United Chemicals, Pool pool stain treatStain Treat is sold in individual Pool Spotting Bags and also in a 2lb jar. A mixture of Oxalic Acid, Pool Stain Treat is suitable for local stain treatments, but may be to expensive for an entire pool treatment. It will even (almost) remove rust stains.

Oh, if you have rust stains, you may need to inspect close up, to determine if metal shavings got into the pool, or if one of the rebar tie wires in the pool shell is rusting through from the inside out! If you have a rebar rust issue in your pool, try using the EZ Patch #7 Rebar Rust Repair Kit.

Identifying and removing a pool stain can be a frustrating experience. It is slow, imperfect and less than what a customer may have thought was possible. Painting a pool can be an option for stain removal (or covering up), but once you start painting, you will need to repeat the process every so often.

Pool Stain Identification: 

First of all, you should determine if the stain is Organic or Mineral.

Organic pool stains come from materials including the remains of leaves, algae, worms, and other animals. These will produce a green, brown or black stain usually. Organic stains tend to be more widespread throughout the pool.

Mineral pool stains in a pool can take on many colors and may be isolated in small areas (pool rust stains) or spread throughout (copper pool stains). They may also be isolated in small crevices or etched spots of the pool plaster.

Many people think that their pool plaster is stained, when they really just have an algae problem. If the stain brushes off, even slightly, or responds at all to shocking or sprinkling granular chlorine over it, then what you most likely have is an algae bloom. Visit our Pool Info page for more information on how to treat pool algae.pool
stain id kit for pool stains

If it's not algae, it most likely is a mineral stain. But further identification is indicated. Introducing the Jack's Magic Stain ID kit. It has four topical tests to determine the type of pool stain you have. Whichever of the four removes your stain - this tells you what type of stain it is, and what product to remove it with. Works on all pool types. The pool has to be 70 degrees or warmer and their are some other specific pool stain testing instructions $10 ea.

Sometimes, You will not have a stain at all, but just normal mottling of the plaster. Remember that plaster is a natural product and is subject to variations in hue and shading. Streaks or mottled effects are considered natural, and they cannot be removed. Sometimes a pool owner needs to just accept a few stains or discolorations. Others find this difficult to do, and insist on a spotless, stainless swimming pool. If this is you ~ fear not, there will be a solution for you. But be patient, as there are frequent setbacks in stain identification, removal and sometimes a recurrence.

What is distinct about an organic stain on your pool is that it can usually be removed fairly easily with a granular chlorine shock (plaster pools only). Just sprinkle over the affected area, and brush with your pool brush. If that works, great! Just shock and go! If not, then we have some more detective work to do!