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Spa or Hot Tub Stain Problems

Spa or hot tub staining or discoloration solutions.
The Pool and Spa Informational Website

Treating Spa or Hot Tub Stains and Discoloration.


Scroll down to browse through some archived SPA and Hot Tub questions and answers.  Please click the Spa Topics Link, on top of every page, to access a complete listing of Spa and Hot Tub Problem subjects, an alphabetized Website Table of Contents, Spa and Hot Tub Equipment Information, About Alan Biographic Material and a Spa and Hot Tub Glossary. Use the other links to access additional subject information. More information about some new and unique products, for Spas and Hot Tubs, can be found by visiting The Website Store. You'll never know what you'll find and that's always fun. Be better prepared and avoid costly problems!

METALTRAP Filters remove iron, copper and manganese. Dual-Cartridge Filter System.
Metal Trap Stain Remover Liquid MetalTrap
Ultra Poly One Coat - before and after pictures. The proper treatment of spa or hot tub staining problems begin with a water analysis, to better understand the nature of the problem.  The proper use of the right chemicals can solve virtually all spa staining and discoloration issues.  Don't let unwanted metals ruin the appearance. ColorQ digital water analyzer.

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How to treat iron, copper, manganese or heavy metal discoloration or staining problems, in spas, swim spas or hot tubs?  Dissolved metals content in spa or hot tub water can lead to staining of the underwater surfaces, discoloration of the water or the appearance of dark to black colored spots. Control of trace minerals and maintaining a proper overall spa or hit tub water chemistry is important, to help assure optimum water quality. Minerals such as iron, manganese and copper are the principal offenders. Iron and manganese can occur naturally in water, especially well water. It is the oxidation of dissolved heavy metals that can cause the spa staining and water discoloration problems, upon the addition of oxidizing spa chemicals. Copper is rarely found in municipal water supplies and usually finds its way into spas and hot tubs as the result of corrosion of the copper heater core or copper plumbing. Treatment of the resultant problem is usually possible with the proper techniques and chemicals. Heavy metal staining and discoloration can be removed, treated and prevented, with the use of METALTRAP Products, such as Liquid METALTRAP, METALTRAP Filters, METALTRAP 1-Micron Pre-Filter and POOL REFRESH.  When the new source water contains sediments, a METALTRAP Dual-Cartridge Filter can removes both the precipitated metals, as well as the dissolved metallic ions, greatly reducing the risk of staining and discoloration. If problems arise, refer to the Spa Problems Page, as a source of problem-solving information, broken down into various categories.  Scroll down the page and click on the linked keywords, catch phrases or images, in the archived answers below, to access additional information, on that topic or product.

Do you know what's in your water?  If you're having problems, with stains and discoloration, due to the presence of metals, you should be testing for iron and copper, to better understand the extent and cause of the problem.  This helps select the best treatment option.  Understanding the nature of the problem, should be step one.  For information about our full selection of testing options, visit our Test Equipment Store.  For information about treatment options, visit our Stain Treatments Store.

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▼     Helpful, Problem-Solving Information, in a question and answer format.     ▼

Treating Iron Stains, When Using A Mineral Sanitizer?

I have a 2004 model spa.  I use a Mineral Spa Sanitizer and change the water every 3-4 months.  In the past 6 or 7 months, Iíve started to get rust stains on the spa surface near the continuous circulation outlet (the outlet where ozonator bubbles come out).   What is the likely source this staining. Thanks.

Keith, 1/27/2018

MetalTrap Stain Remover.
What you are describing sounds like iron.  Possibly, it is present in the source water used to fill the spa.  The fact that you are using
a mineral purifier limits the treatment options.  Adding a stain remover and a chelating agent will eliminate the stains, but it will inactivate the metallic ions, from the mineral purifier.  You should clean the spa with some MetalTrap Stain Remover and drain completely.  Attach a MetalTrap Filter to the garden hose and refill the spa.  As water passes through the cartridge-like MetalTrap Filter, iron and other heavy metals will be removed.  A MetalTrap MT-10 Filter will remove up to 1 PPM of metals, from 10,000 gallons of water.  The MetalTrap Filter should be used, whenever new water is added, and will last for years.  I hope that I have provided the solution.
Sincerely, Alan Schuster, 1/27/2018

Underwater Stains and More?

I have a 375 gallon spa and have noticed considerable calcium build up on the walls of my spa. I just drained and cleaned the spa and could not get much of the calcium off the walls and jets. I have noticed that after about two months, the spa water, while clear when still, turns milky when the air is on. The calcium hardness right now is at about 100.  What can I do to get the stains off the walls and jets next time I drain and clean the spa and how can I keep the water from turning milky after about two months?

Wayland C., 1/13/2017

You seem to have several things going on.  With a calcium hardness of 100 PPM, there should be no scaling.  The cloudy water is probably the result of silt, being raised from spa floor.  You might need a new filter cartridge, to improve filtration.  The stains could be due, to iron.  Calcium scale is not colored.  Have the spa and source water tested for copper and iron.  Stains can be removed with a MetalTrap stain Reversal kit.  If the source water contains copper or iron, I suggest using a MetalTrap Filter to treat the water, as it is being added to the spa.  The milky water could be the result of inadequate sanitation.  The addition of a Spa Nano-Stick Clarifier can help remove fine particles, that frequently pass right through some filters.  Are you able to maintain a stable level of sanitizer?  If not, you need to pay more attention to this task.  I hope that this information will be helpful.

Sincerely.  Alan Schuster, 1/13/2017

Black Ring Around The Tub?

We have not used our vinyl-lined hot tub for a number of months but it has been running and we have added chemicals and dichlor as needed. However it has developed a Black Ring at the waterline, which we cannot remove from the vinyl liner.  We are changing the water, have used a spa cleaner, to clean the plumbing etc.  However, the Black Ring is resisting all attempts with cleaning pads, cleaning products and baking soda, to remove it. Any help would be great. The hot tub is about 9years old.  Thank you.

Graham S., 1/6/2015

Most likely the water contains copper, iron and other minerals. Test the tap water used to fill the spa for copper or iron, which are associated with
Stain Reversall Kit. stains. Copper can also be the result of heater corrosion, due to a low pH. Some mineral sanitizers can add copper, as well. The metals in the spa water may have precipitated onto the walls and resulted in stains and discoloration, which are rarely removed by simply adding a metal treatment or using common cleaners. Try this. Make a paste of some 500-mg vitamin C tablets and rub onto a stained area. If this works, the problem is positively due to metals.  Add 1/2 pound of MetalTrap Stain Remover in a white sock, shut off the filter and scrub the walls. If the stain is removed, repeat elsewhere, as needed. ADD A DOSE OF Liquid METALTRAP FOR EVERY 0.5 PPM OF IRON OR COPPER. Liquid METALTRAP is phosphate-free and does not lose effectiveness at a pH of 7.8 or higher, as do most other metal treatments.  If the stained area is too broad to be treated with the "sock", it may be necessary to lower the pH to 6.8, discharge all of the chlorine and add 1/2 pound of ascorbic acid. Wait 24-hours, after the addition of Liquid MetalTrap, before restoring the chlorine level. Thereafter add a dose of Liquid METALTRAP monthly or prior to adding new water, in order to avoid a recurrence.  I hope that I have been helpful.  If so, please tell your friends and dealers about the website.

Sincerely.  Alan Schuster, 1/6/2015

The Best Way To Treat Well Water?

We have just purchased a new spa and have already gone through the hassle of filling it with well water (big mistake!)  For the past month or so I have been playing the filtering game, cleaning iron covered filters, adding special chemicals to clarify etc. etc.  I plan on getting my water shipped in the next time we drain and fill the tub.  However, I would like to be able to "top off" in between draining and filling.  My thought was to purchase the METALTRAP 1-Micron Pre-Filter, for Spas & Small Pools Item # PS-SF and the Liquid Metal Trap, 1-Quart Bottle Item # LMT-10.  Is this the best approach, or is there something better that I should be using?  Any advice would be greatly appreciated!  Thanks in advance.
MetalTrap Dual-Cartridge Filter, for pools and spas.
Todd D., Geneva, Ohio, 10/17/2014

The 1-micron will not remove the dissolved metals, just the sediments.  A MetalTrap Dual Cartridge Filter System will remove both the sediments and the dissolved metals.  Add a few ounce of Liquid MetalTrap before adding chemicals, for added insurance.  The sediment cartridge is washable and reusable.  The MetalTrap cartridge is replaceable.  You should get many years of use, out of the product.  All you have to do is attach it to the garden hose.  I hope that this will help solve the problem.

Sincerely.  Alan Schuster, 10/17/2014

Stain Ring Around The Spa?

We have a spa in Illinois that is almost a year old. We took care of it over the summer as directed and just drained cleaned and filled it for fall. After adding some ph decreaser and starting some testing we noticed a rust colored ring forming we go it off, and did some more testing and it came back. We are currently draining again to refill. Can you help tell us why this happened?

Amy S., Illinois, 9/17/2013

Most likely the water contains iron and other minerals. Test the tap water used to fill the spa for iron, which is associated with rust colored stains. The metals in the spa water may have precipitated onto the walls and resulted in stains and/or discoloration. Another option
Stain Reversall Kit. would be to use the METALTRAP Filter, as it can remove metal, before they get into the spa. The stains/discoloration are probably due to iron, copper and other trace minerals and are rarely removed by simply adding a metal treatment. Try this. Add 1/2 pound of MetalTrap Stain Remover in a white sock, shut off the filter and scrub the walls. If the stain is gone, repeat elsewhere, as needed. ADD A DOSE OF Liquid METALTRAP FOR EVERY 0.5 PPM OF IRON OR COPPER. Liquid METALTRAP is phosphate-free and does not lose effectiveness at a pH of 7.8 or higher, as do most other metal treatments. At the very least add two doses. If the stained area is too broad to be treated with the "sock", it may be necessary to lower the pH to 6.8, discharge all of the chlorine or bromine and add 1/2 pound of MetalTrap Stain Remover. Thereafter add a dose of Liquid METALTRAP monthly or use the MetalTrap Filter, prior to adding new water, in order to avoid a recurrence. I hope that this information will prove helpful.

Sincerely.  Alan Schuster, 9/17/2013

Should you be testing your water, for  Iron and Copper???

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ColorQ Copper 5 MetChek Test Kit ColorQ PRO 9-Plus
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Using The Right Pre-Filter?

I bought a pre-filter (carbon). The vendor told me it was good for about 3 refill of my spa (450 gallons). I used it once and it doesn't work anymore (water don't go through anymore), but my water has never been so clear! I think I have a lot of copper in my water because it was always green when I filled it before using that pre-filter. I'm thinking buying the "MetalTrap 1-Micron Pre-Filter, for Spas & Small Pools". Do you think it will be usable for a couple of refills? I know it says 10 000 gallons, but I want your opinion on it.

Isabelle E., Canada, 10/27/2009

The METALTRAP 1-Micron Pre-Filter will remove ultra-fine particles and many microorganisms. It is particularly useful
where the source water is of poor quality. It should be able to be used to refill your spa up to 20 times, depending of the nature of the source water.  However, your description of the water color and the mentioning of a copper possibility, leads me to question, whether a METALTRAP Filter would not be a better choice. The METALTRAP 1-Micron Pre-Filter will remove the metals that have precipitated, but not those in solution. The "green" color could be copper or iron or both. The METALTRAP Filter will remove all the dissolved metals, and will save you from having to deal with discolored water and stained surfaces. The METALTRAP MT-10 should be able to be used up to 20 times to refill the spa. You can always test the water, before and after, to confirm the Filter is still effective. The best way to deal with metals is to physically remove them from the water and not with chemical treatment. I hope that this information will problem helpful.

Sincerely. Alan Schuster, 10/27/2009

Is It Black Algae?

I have read all the problems submitted by others. Our discoloration is mostly dark green with many, mottled black spots. The green looks like oxidized copper. Is it still considered "black algae"? If so, what do you recommend?

Alan G., 6/16/2010

It is extremely unlikely that the problem is black algae! It could very well be a copper stain that resulted from corrosion of the copper heater core. Ask your self the following questions? Is chlorine or bromine being used? Has the pH been below 7.0, for extended periods of time? Are you placing chlorine or bromine in the skimmer? I suggest that you have the water tested for copper. If present, that will conform the corrosion. You will have to treat and clean the spa. METALTRAP Stain Remover can be used to remove stains. After the removal, either drain and rinse the spa or add a dose of Liquid METALTRAP. If corrosion was the cause, you need to pay more attention to the pH and total alkalinity of the spa water. I hope that I have been of assistance.

Sincerely. Alan Schuster, 6/10/2010

How to deal with metals, stains and discoloration.

These products remove metals and avoid future, recurrent problems.
Don't just treat stains . . . eliminate them and prevent their return!!!
Stain Reversal Kit. Liquid MetalTrap MetalTrap Stain Remover. Pool Refresh eliminates phosphates and metals, from pools and spas.
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MetalTrap Dual-Cartridge Filter, for pools and spas. MetalTrap Single-Cartridge 5-Micron Filter System, for pools and spas. MetalTrap Filters remove heavy metals. MetalTrap 1-Micron Pre-Filter, for Pools and Spas.
Filter System
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Visit The Metals and Staining Treatment Store for complete information.

Discolored Water?

I have a 275 gallon spa and recently I emptied, cleaned and refilled the spa. I added the chemicals (bromine) in the usual way and the spa water started to turn brown in color. I brought a sample into a local dealer and he said that it was iron. It never happened before. Can you explain this?

M. L., 12/17/2016

Liquid MetalTrap
Where did the iron come from? That's the real question. If iron is not normally present in your household water on a regular basis, it might have ended up in your spa water because a fire hydrant was opened somewhere, up line, in the neighborhood. That caused sediments to be lifted off the bottom of the pipes and the rest you know. It is also possible that your water does contain an occasional trace of iron, depending upon the conditions at the water source, rainfall amounts, etc. Knowing the amount of iron present is helpful. Make sure that you add a quality metal treatment, such as Liquid METALTRAP, in sufficient quantity, for the amount of iron present. Add another dose monthly and prior to the addition of makeup water. The hope that this information cleared things up for you.

Sincerely. Alan Schuster, 12/7/2016

Water Turned Purple?

I just changed the water in my hot tub and it is purple. I've had the spa for 5 years and this is the first time anything like this has happened. The water came out of the faucet clear and after I balanced it, the water turned purple. The only thing that was done differently this time was I used a pre-filter to eliminate the iron ring after filling. Is the water good and will it clear up? Any help would be appreciated. Thanx.

Mike C., 11/8/2011
MetalTrap Dual-Cartridge Filter, for pools and spas.
Most likely the water contains iron, manganese, copper and other minerals.  Purple suggests manganese and copper. Test the tap
water used to fill the spa, as chemicals in the spa water may interfere with the test. The metals in the spa water may have precipitated onto the walls and may not show up in a water sample. A good option would be to use the METALTRAP Dual-Cartridge Filter System, as it can remove metals and minerals and contaminants, before they get into the spa. ADD A DOSE OF Liquid METALTRAP FOR EVERY 0.5 PPM OF IRON OR COPPER. Liquid METALTRAP is phosphate-free and does not lose effectiveness at a pH of 7.8 or higher, as do most other metal treatments. At the very least add two doses. Thereafter add a dose of Liquid METALTRAP monthly or prior to adding new water, in order to avoid a recurrence. I hope that this information will help clear things up.

Sincerely. Alan Schuster, 11/8/2011

Only The Spa Is Stained?

I recently purchased an iron test kit from your site, so I'd appreciate a bit more help. Enclosed is a picture of spa water which occurred when the spa person washed the spa filter in muriatic acid and then thoroughly rinsed it. There have been red rust stains on the spa. Cistern water tests "no iron" but water you see in the spa tests 0.3 iron. The spa uses bromine. The pool which uses salt chlorination and shows no rust stains. I've just replaced the spa gas heat exchanger (now cupronickel) and there's no other source of rust. The whole house water filter DOES, however, fill with a reddish material on the 1 micron filter we use to filter it out. We believe that the dirt on the hillside in the Virgin Islands (red) has a lot of iron in it. Please answer this: Why does the spa show iron stains and not the pool? Does the bromine precipitate any iron that is in the water? Does salt generated chlorine not precipitate iron so the pool does NOT get stains? Do you think we need a specific iron filter? Thanks.

Norm, Virgin Islands, 4/30/2017

Red colored soil usually is high in iron. There is a possibility that copper is interring with the iron test and is showing up as iron. What I see in the spa are not iron stains. Copper stains from corrosion of the heater core are more likely. The action of chlorine or bromine, upon iron
Stain Reversall Kit.or copper is virtually the same. Iron stains are yellow to rust colored. Copper stains are blue-green to black. You replaced the heater coil, why? The pool operates with a salt chlorine generator and low pH is rare, because the SCG drives up the pH. Bromine or chlorine will not attack copper unless the pH is acidic. Most likely the pool's pH is always around 7.8 or higher. The spa is using bromine and bromine tablets are acidic. If the pH drops below 7.0, corrosion and staining could result. The photo seems to show that. If you used bromine tablets and did not add pH Increaser on a regular basis, your pH was too low. I think you need to do the following. Add several doses of phosphate-free, Liquid METALTRAP, to the pool and spa. Add another monthly. Use a METALTRAP Filter, while adding any new water to the pool or spa, to help remove particulated iron. For cleaning of the spa stains try using a solution of METALTRAP Stain Remover. Refer to the page on pool staining problems, for more on this topic. I hope that this information is helpful.
Sincerely. Alan Schuster, 4/30/2017

Turned Brown?

We were changing the water and we added the calcium hardness treatment. Then we add the bromine and it turns brown. We have changed the water regularly and this has never happened before. What is wrong?

Linda M., 4/15/2007

This sounds like a spa, but you didn't make that clear. Either way, everything applies. Pools/spas that turn color after bromine has been added usually have a metals problem. This can be very common with well water. ASAP add at least a double dose of a quality metal Treatment, such as phosphate-free, Liquid METALTRAP. This might help avoid staining and should make an improvement. Bring in a water sample to a local dealer and have the water tested for iron, copper and other parameters. I suggest adding a dose of metal treatment for each 0.5 PPM of metals. Add another dose prior to adding new water. A monthly dose is an additional safeguard against a recurring problem. To help avoid such problems, I suggest using a metal removing pre-filter It can remove much of the metal content and help avoid such problems. I hope that this information proves helpful.

Sincerely. Alan Schuster, 4/17/2007

Black Spots?

My spa and pool are 4 years old. I have been treating my spa for what I thought was Black Algae for the last five weeks. The temperature finally cooled off so I could empty it and scrape off a sample. I took the sample to the pool supply place and they determined it was metallic. There are two spots, about the size of silver dollars, on the side of the spa. What could be causing this? Thank you.

Jake G., 10/29/2008

Metal Trap Stain Remover
The stains could be the result of copper, in the presence of high levels of calcium hardness. The copper could have come from corrosion of the heater. Assuming that the spa and pool are gunite, try putting about 1/2 pound of pH reducer in a sock and place on a spot. Leave in place for about 30 minutes. Hopefully, this will dissolve the upper layer of plaster and remove the stain. Sometimes, it is necessary to use METALTRAP Stain Remover for this purpose. Sometimes black spots form, as a result of the use and abuse of calcium chloride in the plaster mixture. This problem was well described in the 1/15/03 issue of Service Industry News (Carlsbad, CA). If this is the case, there is nothing that is known to eliminate the problem, short of refinishing. I hope that the information will prove helpful.

Sincerely. Alan Schuster, 10/29/2008

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Green Gunk?

We have a fiberglass spa (500 gal) and it has developed green "gunk" (for lack of a better description). This stuff is in small chunks and adheres to the sides of the tub, our suits, of course it's filling the filter and it's covering the plastic parts of the filter. If it lands on anything while hosing out the filter, it sticks like glue.  It can be scrapped off the tub and filter. What caused it and how do we get rid of it? We switched from bromine to chlorine, could that have caused it? We drained and cleaned the tub and filter before switching. Thanks.

Kay and Jim, Florida, 3/10/2012

This "green gunk" could be copper, resulting from corrosion of the filter. Not a good thing! Have you been failing to maintain the pH at 7.2-7.8? Low pH conditions will corrode the copper heater core, in the presence of chlorine or bromine. Chlorine tablets should not ever be used in a spa, especially not in the skimmer. I suggest that you have the water tested for copper. If present, it is the result of corrosion and low pH. Add a double dose of a quality metal treatment, such as phosphate-free Liquid METALTRAP, and make sure that the pH is 7.2-7.8, at all times. You might be better off draining the spa, if my assumptions are correct. Otherwise, get back to me with the actual water analysis results and the type of chemicals being used. Have you ever considered an ozonator? It will make spa maintenance easier and produce better water quality, with fewer chemicals. I hope that this information will prove helpful.

Sincerely. Alan Schuster, 3/10/2012

Black Deposits?

I am in Lake Tahoe, Nevada.  I operate an indoor swimming pool and spa at an estate.  Neither the pool or the spa gets used much. I am having a problem with the spa.  On several occasions I have found a very black substance that almost appears to be a fungus that is attacking the chrome vents on the sides and bottom of the spa.  The spa is made of imported tiles and the black substance always starts at the chrome and begins traveling into the grout lines. Today, I drained the spa and sprayed household bleach on the spots.  It did nothing and I then sprayed Muriatic acid on the spots and they dissolved. I just purchased a 9-way test kit so I can get specific readings for pH, hardness etc. I'm not sure where to go from here. The local pool guy had no idea what this problem could be.  Any help would be greatly appreciated. Regards.

Tim M., Lake Tahoe, NV 5/11/2004

The problem is positively not a fungus, mold, mildew, algae or bacteria. Otherwise the liquid chlorine that you sprayed on would have had a positive effect. The fact the muriatic acid dissolved the black deposits means that the problem is due to a metallic or mineral stain. There are a few possibilities. The water used to fill the units may contain trace amounts of iron and other heavy metals. Testing the spa water as well as the tap water can help conform this possibility. In any event, because it is a metal or mineral problem, I suggest that you add a dose of a quality metal treatment, such as phosphate-free Liquid METALTRAP, on a monthly basis and prior to the addition of any new makeup water. The other possibility is that the deposits are being caused by the oxidation of the products of corrosion. The copper heater core and other metal parts might have been subjected to the corrosive forces of acidic water conditions. Copper can cause dark stains in the presence of high levels of calcium hardness, although high calcium, by itself, will not cause such a problem. Make sure that the pH remains in the 7.2-7.6 range and the total alkalinity is not below 80-120 PPM. Either or both of these possibilities could have been the cause and these steps should help avoid a recurrence. If you are using trichlor, make sure that the feeder in plumbed after the heater and that there is a check valve between the two. I hope that this information proves helpful.

Sincerely. Alan Schuster, 5/12/2004

Blue Stains?

I have some blue-colored stains near some jets and on the bottom. Could this have been caused by copper? The spa is about 300 gallons and is about 12 years old. I use bromine tablets and a non-chlorine shock. Is there anything that I can do? Thanks.

Anthony N., VT, 10/30/2010

The blue-colored stains are probably due to copper. The likely source is from your heater. If you're lucky, the damage to the
Copper test kit for pools and spas heater was not serious. You didn't mention that there was any discoloration of the water, so I will assume that there was none. That being the case, you probably don't have much copper in the water. A Copper Test should confirm this. To avoid staining, I suggest that you add a dose of a quality Spa Mineral Treatment, such as phosphate-free, Liquid METALTRAP, to the spa water. The next time that the spa is emptied, try cleaning the stained areas with a solution of METALTRAP Stain Remover. Make sure that you use rubber gloves and eye protection. Rinse any metal parts with water, to remove the chemicals and the dissolved stains. Rinse spa clean before it is refilled and don't forget to add a dose of the Liquid METALTRAP, as it is being refilled. The cause of the copper problem was probably due to corrosive, low pH conditions. In the future, make sure that the pH remains in the 7.2-7.8 range. To help stabilize the pH, the total alkalinity should be 80-120 PPM. I hope that I have been helpful. Keep enjoying the spa.

Sincerely. Alan Schuster, 10/30/2010

Stain Removal In Pool-Spa Combo?

I have a large in-ground pool/spa, 7 years old, kidney shaped, about 30,000 gallons. It has had a Copper Ionization + ozone system on it for about 5 years. Over the years, the pool service did not maintain the pH properly and the pool has developed gray stains. A drain and acid wash is recommended by my pool service but I am reluctant to proceed due to the expense and the impact it has on the pool surface finish. My pool technician, has suggested that he has been successful in treating stains like these with the addition of Muriatic acid to the water. I am willing to give this process a try as it appears cost effective and should not damage the finish. I would like to try the treatment on the spa first, and see if it is successful. If yes, than I would like to do it to the whole pool. What are the pros and cons to this approach? How much Muriatic acid needs to be added for success? My spa is 8 feet in diameter. How many gallons of acid for the 30,000 gallon pool? How long should I let this circulate? Are there different strengths of Muriatic acid? Which one should I use? What is the best way to restore the water chemistry after this operation? Thanks.

M.B., 10/24/2007

A pool or spa be subjected to an acid bath as a means of stain removal. Basically it dissolves the top surface and hopefully takes the stain with it. Lowering the pH will subject the metal parts to corrosion, including the heater, if chlorine or bromine are present. Therefore, treatment should be in terms of a short period of time - a day or less. This is important to help minimize the possibility of excessive surface etching. You have to add enough acid to lower the pH just below 7.0. A pH of about 6.8 should suffice. Use the brush to scrub the surface. Bypass the heater, if possible. A better and safer method is to use the METALTRAP Stain Removal System. Once the discolorations and stains are removed, use The METALTRAP Filter, for all future water addition and the problem should not recur.  Restore the pH and TA. Because the addition of the metal treatment will interfere with the copper being introduced by the ionization unit, I would recommend using a polymer algaecide for a month or two, while the copper ion content is re-established. I hope that this information proves helpful.

Sincerely. Alan Schuster, 10/24/2007

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