Miscellaneous Pool Algae Problems

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It is not always possible to identify a type of algae without microscopic examination and this, of course, requires a trained individual. Most algae problems involve green water, cloudy or hazy water, slimy walls and surfaces and a lack of adequate pool water sanitizing. Most algae problems respond quickly to proper treatment. However, if current attempts to control an algae problem are not meeting with success, the problem should be considered to be that of a resistant-algae condition and should be treated in a manner similar to black algae. Water mold and slimes can be treated in a manner similar to that of "Pink" algae. Algae can be controlled with various products including: swimming pool sanitizers, algaecides, shock treatment and phosphate eliminators. Adding some backup sanitizing can work wonders.  Consider adding something such as a Salt Chlorine Generator or Ultraviolet Sterilizer.  Sometimes a combination of products must be used together to achieve the desired outcome.  The use of The Circulator, as a replacement for standard return jet fittings, can dramatically improve circulation, better distributing sanitizer to all areas of the pool.  If problems arise, refer to the Pool 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.

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► Algae or Mold?

Mold is growing in our salt water pool. I have tested the water and my free chlorine is 0.5 TCL is 0.7 PPM.  pH is 7.9.  Alkalinity is 149 PPM.  Cyanuric Acid is 10. Calcium hardness is high.  Could you tell me what chemicals I need to add?  Thank you.

Stacie, 7/29/2018

Mold or algae, either way you need to do the following.  Raise the free chlorine to 10 PPM and keep it a 5-10 PPM, until the problem is eliminated. Get the pH down to 7.2-7.6 and keep it there. Increase the cyanuric acid to 30 PPM. Once the problem is solved, keep the free chlorine at 2-4 PPM and the pH at 7.2-7.8.  Improving circulation can eliminate the dead zones that promote algae and mold growth. Replacing existing return jet fittings with The Pool Circulator will make a dramatic improvement.  Please visit our website store to browse through a large selection pool and spa water testers, as well as many different, useful and interesting pool and spa products. Many are on sale now.  I hope that this information is helpful.

Sincerely.  Alan Schuster, 7/29/2018


► Slimy Blobs?

Dear Alan. My question: One of my accounts has a saltwater system, when I took the account the owner only had a chemical checking company and no cleaning. When I arrived to bid the account and look things over, I found that he had this stuff growing on the first step and a few other spots in the pool that looked like blob something or other. Remember magic rocks how they grew from the bottom of a container, well that's what this looked like but clear and slimy. Could you tell me what it is ? And what causes it and how to prevent it from happening again? I seem to have it under control, still having problems with spots that are not black algae. Kind of like stains seeping through the plaster. Owner had a acid wash a few years ago and now stains are appearing. Thank you so much for your advice, your site is very interesting, I have been reading for the last 2 hours.

Ronda V., 10/1/2017

The slimy blobs were probably algae, mold or some other microorganism. This type of problem can develop, if the chlorine level is not properly maintained and will first occur in areas of poor circulation. Now that the situation is under control, try and redirect the return flow to send more water towards the effected areas. Test the salt level and make sure that it is adequate for your salt chlorination system and that it operates properly and for reasonable periods of time. In addition to this problem, you may have another concern. The dark spots could be a mineral stain and can be treated with a MetalTrap Stain Reversal Kit, if due to metals. Refer to the archives on pool staining for information on the sock trick. Another possibility is the use and abuse of calcium chloride in the plaster mixture. An excellent article appeared in the January 15, 2003 issue of Service Industry News.  If this is the case, there may be no simple solution. I hope that this information will prove helpful.

Sincerely. Alan Schuster, 10/1/2017


► All Algae Are Not Created Equal?

A week or so ago, you helped me identify a pool water problem that I had been fighting for several months. You advised me that I should be killing "mustard Algae" (not green algae that I thought was my problem and so did several other local "experts"). Thanks to you and your expertise, and following your instructions I now have a clear, algae free pool. You were absolutely correct, my problem was mustard algae and NOT green algae. The shock treatment and the sodium bromide made a big difference. You deserve more than just a thank you, but that is about all I can pass along to you. Thank you!

Bill T., Sun City West, AZ, 9/22/2016

Thanks for the follow-up. Glad to hear that everything cleared up. Yellow mustard algae can be a tough one, especially, if you are not familiar with the problem. So don't be too tough on the "locals." Enjoy the summer!

Sincerely, Alan Schuster, 9/23/2016


► Phosphate Eliminators And Algaecides?

Every now and then I get a touch of a greenish water and algae. Some algaecide and shock, is all that it seems to take. Is there some advantage to using a phosphate eliminator? How does it differ from algaecides? 

F. T., Coral Springs, FL, 8/20/2013

Phosphate Eliminators are typically used in conjunction with algaecide and standard swimming pool maintenance. When added to a swimming pool, POOL REFRESH reacts with the phosphates and drops their concentration from parts per million to parts per billion. The presence of phosphates and nitrates can accelerate algae growth and increase the chlorine demand. Some dealers can perform these tests and it can be worthwhile. Phosphates are a vital nutrient for all types of algae and their almost total removal from the water interferes with the ability of algae to grow and thrive. While you can't remove the nitrates in any practical way, eliminating the phosphates can make nitrates less of a problem, by denying algae a vital nutrient. Literally, the algae starves to death! No algae - no problems with green water. All this sounds great, but as long as you have people in swimming pools, there will be phosphates added in some quantity. For this reason the phosphate eliminator has to be added on a periodic basis. A phosphate test can be performed occasionally to determine the need to add additional product. As additional assurance against algae growth, it is a good idea to maintain the normal additions of algaecide. The product is a worthwhile addition to the anti-algae arsenal. The only downside is that its initial addition will result in a precipitate that has to be removed by filtration and/or vacuuming. Subsequent product additions are much less of a problem because of the reduced phosphate content of the water. BETTER CIRCULATION CAN SOLVE A HOST OF PROBLEMS. With The Pool Circulator you can improve the circulation, dramatically, simply by replacing the return jet fittings. I hope that I have satisfactorily explained the product. Enjoy the summer.

Sincerely. Alan Schuster, 8/20/2013


► Biofilm?

Hi Alan, your website is very good and I have purchased one of your books. I have a problem, though, that I haven't encountered in any of the topics on your site. I have a rectangular pool; 18' x 36' x 10'deep. About 34,000 gals. A week or so ago, I noticed a small mustard algae problem--only several patches. When I opened the pool this year (I live 40mi. north of the  New Orleans area, and in the winter, all I do is cover it, run the pump 5hr./day, and check for balance every couple of weeks), I didn't add any algaecide. Being the over-achiever that I am, I figure I'm going to hit this problem hard and go out and buy a 50% Algaecide . It's the quat-type algaecide. After adding the recommended dose for visible algae: 14oz. per 10,000gal, I am horrified! My water turned milky ,foams when agitated, and has a terrible odor--kind of like mildewed plastic. I should've just shocked a couple of times, I guess. Here's the scary part; on the walls of the skimmers, I discovered a slimy film (and a lot of it) with the consistency of wet modeling clay, evidently the result of the foaming action taking place inside the skimmer.  AND IT'S NOT WATER SOLUBLE. What the heck is this stuff doing' to my sand filter? I shocked the pool right before adding this stuff, and shocked again a couple of days after. My pool water was like a diamond before I put this stuff in. I'm ready to go to the chemical people and strangle the first person I see. Please tell me that the water is going to clear, the smell is going to go away, and that the sand in my filter doesn't look like bearing grease. Thanks for any answer that you can provide.

Jimmy L., Covington, LA, 5/19/2020

You have several thing which have come together. During the winter, a biofilm developed. This is the slimy stuff on the underwater surfaces. It is comprised of microorganisms that grew in the absence of adequate chlorine levels.  Quats (I hate them) may not kill the biofilm and certainly won't decompose it. At best, it attaches to the biofilm and impedes its growth. It also causes unsightly foam. The water was clear before the quat algaecide was added because the biofilm was on the walls and not in the water. Adding the algaecide caused the foaming and may have caused some of the biofilm to enter the water. All you should need to do is add shock and boost the FREE CHLORINE level to 5-10 PPM. Retest often and add more chlorine, as needed. Don't drag it out! Once you have established a persistent FREE CHLORINE level, the biofilm should have been destroyed on all of the under water surfaces, including the filter. Keep an eye on the filter pressure and service accordingly. Reliable testing is important, so I suggest using a ColorQ 2X all-digital tester, which eliminate all color-matching and guesswork. During this period keep the filter going 24/7. Once solved, resume normal pool operation. I hope that this information proves helpful.

Sincerely. Alan Schuster, 5/19/2020

► Resistant Algae?

I have a 16,000 above ground pool and I am getting what appears to be black or dark brownish gold mustard algae in the ends of my pool, more prevalent in the shallow ends of the pool. The deeper section is in the middle and seems less likely to be affected.  I have a DE filter (running about 8 hours and the cleaner runs 3 hours) and the problem seems to have begun when the water temperature reached 69 degrees. I have shocked the hell out of the pool and when I sprinkle the granular shock on the deposits it clears up for a day and then begins reappearing. I tried treating with black out, and then with some yellow algae treatment. The yellow required I raise the pH to 8.0 and treat and shock and treat and shock 12 hours later and then shock only again 12 more hours later. That is where I am now, but I don't want to shock again as the pool smells like a bottle of laundry bleach now. There is 4-5 ppm of chlorine, same level of free chlorine. I am thinking after reading your FAQ's that if I have algae growing in my pool of chlorine. Maybe it is metal deposits precipitating out of the water.  The black stuff also is not affected at all by brushing until I shock the hell out of the pool and then most of it disappears for a day or so, but no longer. Any little bit left easily brushes away, but most disperses on its own. I am taking a sample in tomorrow to get the metal contents tested and see if this confirms what I think I read in your FAQ's. In the meantime, if you have any other ideas I am interested in hearing from some knowledgeable parties. I am getting sick and tired of buying anywhere from $40-$100 worth of chemicals that only fixes the problem in most cases for 12 hours. The 16 year old pool experts and the little bit older store managers don't seem to be cutting it for me so far. Anxious in Austin TX>
 
John B. Austin, TX, 4/10/2010

If it turns out that you have a heavy metal problem, it would be in addition to an algae problem. What you are describing does not seem like the classical case of mustard algae. The algae treatments that you have added, probably contain an ammonium salt. This would account for the odorous conditions that you have described. The ammonium salt reacts with the chlorine to form chloramines, an odorous form of combined chlorine. It has been demonstrated the high levels of chloramines can be effective against certain types of algae. After the algae has been destroyed, it is mandatory to shock the pool with large amounts of chlorine in order to destroy the chloramines.  In your case, in would appear that algae is somewhat resistant and is not responding to this chloramine treatment.  I suggest that you treat this problem on the basis of being a resistant algae. Lower the pH to 7.0.-7.2. This will help make the chlorine more effective. Add chlorine shock, at the rate of 2 pounds per 5,000 gallons, until a Free Chlorine level of 5-10 PPM is achieved and persists for an overnight period. It may be necessary to add more shock or make further pH adjustments, because of the prior addition of the other products. The longer this takes, the more chlorine will be required. Operate the filter continuously. Redirect the return flow to send more water to the affected areas. The simple installation of The Pool Circulator: a circulation booster that can help make algae growth less likely, by improving the chemical distribution and eliminating dead spots. The addition of a polymer algaecide will further assist in controlling the algae. Brush the effected areas to help the chemicals reach the algae growths. After the problem has been eliminated, resume normal filtration and chlorination and restore proper pool water chemistry. The practice of sprinkling granular chlorine, directly on the effected areas, is not recommended and could result in damage to the vinyl liner.  I hope that this information will prove helpful. Good luck.

Sincerely. Alan Schuster, 4/10/2010


► Underwater Slime?

I had a new liner, cartridge filter, and an ionizer installed this spring in my in ground pool. The pool is about 22,000 gal. I have a problem with slime on the bottom and sides of the pool. It appears clear, but it makes the pool very slippery and unpleasant. I have tried increasing the level of the ionizer and I have tried decreasing it. It currently reads between 0.2 and 0.3 on the copper ion tester. I have tried to use non chlorine shock and it helps some, but the slime is back in 2-3 days. The pool installer and pool stores around here are no help. Yesterday, I did the shock again and then put in an algae preventer liquid. Today, it still has a little of that slime feel to it. What is wrong? How do I get rid of it? The summer is "slipping" away and my pool is getting unusable. Thank you for your help.

Nameless, 8/4/2005

The slime is a most likely a bacterial film. Copper is recognized as an algaecide and not as a bactericide. I would add chlorine and boost the Free Chlorine to 5-10 PPM. It will kill and decompose the slime. Dealers that sell ionizers may be reluctant to suggest chlorine, as that was part of the reason to buy the ionizer. There is no reason that you can't use chlorine to maintain a 1-2 PPM level: both to oxidize wastes and to act as a sanitizer backup. The presence of the ionizer will allow you to do this with less chlorine product. The recurring nature, of the problem, could be indicative of dead zones and poor circulation. The Pool Circulator is a circulation booster insert, that dramatically eliminates dead zones and makes the water come alive. You'll get better distribution of sanitizers and that should help minimize algae and other related problems. This information should help get you back in the swim.

Sincerely. Alan Schuster, 8/4/2005


► Algae Hideout?

Hi Alan, when I had a swimming pool it used to suffer badly from Algae build up. It did not matter what I did I could not get rid of it until one day the pool light blew. On removal I found a pocket of algae that was the breeding ground. Being behind the light it was never in the moving water and therefore did not get treated. I hope that this knowledge might help some of the visitors to your site who are experiencing algae problems. Regards.

Steve, 3/17/2012

There's no doubt that the colony, in the light housing, was not helping the situation, but it is not that simple.  All pools are constantly exposed to algae at all times.  Only when the conditions are right, will algae bloom.  Having that colony just made things happen quicker, when the sanitizer level dropped too low.  Algae will grow in all the nooks and crannies, if the conditions allow.  Better circulation eliminates the dead zones, that promote algae growth.  Replacing standard return-jet fittings, with The Circulator, can dramatically improve circulation and sanitizer distribution, by as much as 1500%.  Better circulation makes everything better.  Thanks for sharing the information.

Sincerely, Alan Schuster, 3/18/2012


► Draining As An Algae Cure?

If my pool needs to be drained because of algae. Is it harmful to drain my vinyl lined pool? What should I do?

Edward R., 4/7/2009

It would have been helpful to know if your pool was inground or above ground. If it is an inground, draining exposes the pool to the risk of structural damage or collapse. In either case, draining a vinyl lined pool runs the risk of liner shrinkage and should be avoided, unless there is no other option. Algae can treated without draining! Pools neglected for years can clean up, with enough chlorine and some work. Draining a pool with algae will not solve the problem. Proper chemical treatment is needed. I suggest that you remove debris and get the filter running. Add chlorine, at the rate of 1 pound per 5,000 gallons, every few hours until the water improves or there is a stable level of free chlorine, of at least 1-3 PPM. Don't drag this out! Keep testing and keep adding more chlorine, as needed. The longer it takes, the more chlorine will be required. Adjust the pH to 7.2-7.6. Make sure that the filter is operating properly. As the water starts to improve, add a dose of a quality blue clarifier, to help remove fine particles and dead algae. You might rethink how the pool is being sanitized.  A salt chlorine generator would provide better algae control, with less effort and an improvement in the water quality, as well.  I hope that this information will prove helpful.

Sincerely. Alan Schuster, 4/7/2009


► Recurring Brown Spots?

Hello Alan, here's my problem. I keep getting dark brown spots at the bottom of my 21' above ground pool in the nooks and crannies. I've tried shocking, algaecide, vacuuming on waste, but to no avail. I've had the water tested for metal and iron and copper and nothing was found. It keeps coming back no matter how many times I vacuum. Some say it's very fine particles coming from branches of tree above that are so fine they can't be vacuumed. Don't know what or who to believe anymore. Any suggestions on what to try to rid these STUBBORN brown spots? At the end of my rope the past couple years with this problem that no one can seem to fix. Thanks, Al.
 
Steve, 5/13/2008

The fact that is appears in the nooks and crannies would lead to be believe that it is algae. Adding the fact, that no heavy metals were found, algae is looking like the culprit. The problem is that algae grows best in areas of poor circulation and poor chemicalization. Adding The Circulator is the easiest way to improve circulation and chemical distribution.  Your letter implies that "it keeps coming back." Have you ever gotten rid of it? Shocking the pool is a good place to start. Redirect the returns to send more water into the affected areas. The presence of phosphates and nitrates can accelerate algae growth and increase the chlorine demand. Some dealers can perform these tests and it can be worthwhile. You might want to consider using a phosphate eliminator, such as POOL REFRESH. This type of product can help avoid conditions that allow for algae growth. I would discount the particles from the tree theory. Here's another suggestion. Put 1/2 pound of pH decreaser powder in a white sock , shut off the filter and drop on a spot. leave in place for 15 minutes and move around with a vacuum pole. If this works, the problem is metals despite the test results and should be treated accordingly. I hope these suggestions are of help. Browse through related areas of the archives. Good luck.

Sincerely. Alan Schuster, 5/13/2008


► Probably Not Algae?

We just got a new above ground pool(24 foot, 52 depth) and the day we got it installed we had half of the pool filled with city chlorinated water and filled the rest with the hose. The next morning we went and checked on it and it was full of algae. We put 2 gallons of liquid shock and one bottle of algaecide and have had the chlorine tablets in since the tanker left. We are still having problems getting it clean could you give us any advice to what we should do or use. We have also vacuumed it too. Thanx.
 
Kathy, 6/8/2009

It sounds like you used a "hose" with well water to fill the balance of the pool. It is not likely that your problem is algae: it just doesn't grow that fast! Your problem is probably minerals present in the water from the "hose." You need to have the pool water and the 'hose' water tested for iron and other minerals. ASAP, I would add a double dose of a quality mineral treatment, such as Liquid METALTRAP, which is a true, phosphate-free chelating agent. Using a METALTRAP Filter, attached to a garden hose, can remove metals from all the new water being added to the pool. Please refer to the archives on pool staining problems for more on this possibility. Good luck and I hope that I have been helpful.

Sincerely. Alan Schuster, 6/9/2009


► A Fungus Could Be Growing On the Reverse Side Of The Liner?

One of the local pool dealers told me that the problem I am having is not algae or a stain inside of the pool, but is a fungus or something growing on the outside of the pool liner. It looks like a gray shadow or stain and scrubbing doesn't do a thing. Is this possible? What can I do? Have you heard about this before?
 
M.H., Bricktown, NJ, 5/23/2006

Yes and No! It is not very common, but I have heard about it before. Actually, a dealer once took me to inspect a pool: it had a liner held in place with a bead and after pulling it away, there were the black spores - right where the discoloration was on the water side. The cause is the growth of a microorganism, on the reverse side, that has invaded the liner.  Perhaps, by feeding on the plasticizers. Adding chemicals to the water will not bring them in contact, with something outside of the water (the other side of the liner). If the liner gets bad enough and needs to be replaced consider this point. Replacement may only bring a return of the problem, unless the liner has been treated with anti-microbial agents. In any event, I suggest that the pool site be treated with weed killers and herbicides, to add a degree of protection. Another suggestion would be to place the new liner right over the old one. I would run all these suggestions past someone experienced with liners and this problem. I hope that I have help of some assistance. Good luck.

Sincerely. Alan Schuster, 5/24/2006

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