For the past two seasons I've been dealing with really stubborn algae. Its comprised of small black or dark brown spots that always seem to settle in the exact same places so much so that they have created a darkness on the liner where they settle. I am using nothing but chlorine bleach, a gallon or two a day. I have had the pool closed for two year and haven't had time to properly test. I've just been using the small tester for ph and chlorine. The water is very clear. We are vacuuming and brushing frequently but its back within hours. I know I need to check CYA and will today or tomorrow. But I need some help identifying this. Hope I can include the pics I took. Thanks all !
Stubborn Algae
- Thread starter Dave2590
- Start date
- Jun 22, 2014
- 47,752
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Hi Dave! 
The pics are a little hard to ID for me, but based on what you are saying, I'd go with algae. I say that because adding a gallon or two per day as you have been doing tells me some organic material (algae) is tearing-up that free chlorine. My pool is just under 18K and I use 1/2 gal per day in the blazing summer. This time of year maybe a half gallon per week in chilly water. You admit not having tested properly for a while, so I'd look to your trusty TF-100 if you still have it and be prepared to perform a SLAM (link below). Get rid of that algae once & for all. Then your staining and excessive bleach consumption should go away. Hope that helps.
The pics are a little hard to ID for me, but based on what you are saying, I'd go with algae. I say that because adding a gallon or two per day as you have been doing tells me some organic material (algae) is tearing-up that free chlorine. My pool is just under 18K and I use 1/2 gal per day in the blazing summer. This time of year maybe a half gallon per week in chilly water. You admit not having tested properly for a while, so I'd look to your trusty TF-100 if you still have it and be prepared to perform a SLAM (link below). Get rid of that algae once & for all. Then your staining and excessive bleach consumption should go away. Hope that helps.Hi Dave!
Hi Pat,
Here are my test results with the TF-100 kit. Pretty sure the chemicals are stale, maybe you can tell me? Free chlorine 2.5, CC 0, Total chlorine 2.5, Calcium 625, TA 50, CYA 0.
- Jun 22, 2014
- 47,752
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Oooh. Okay. Well, let's try to get you fixed up. Here's a few things to help:
- We never want a CYA of zero, so you'll want to increase it to at least 30. Use granular stabilizer and the sock-soaking method (squeezing often). The Poolmath calculator can help with the amount to soak. Once it's dissolved, consider your CYA 30.
- We know you need to SLAM, so while the sock is soaking the stabilizer, make sure the pH is lowered to about 7.2,, then increase the FC to "12". That will be your FC SLAM level until you pass all 3 SLAM criteria. Make sure to brush the pool, check the filter pressure/backwash, and most important maintain that FC of 12 as best as you can until the SLAM is complete.
- The TA is fine. CH is slightly elevated, but not much you can do. Make sure you're never adding cal-hypo shock products which increase CH quickly.
If the reagents were stored indoors in the shade or cool place, they should be okay. At least to get you through the SLAM. But at some point you know you can always go back to TFTestkits and order some refills when you're ready. Hope that helps.
- We never want a CYA of zero, so you'll want to increase it to at least 30. Use granular stabilizer and the sock-soaking method (squeezing often). The Poolmath calculator can help with the amount to soak. Once it's dissolved, consider your CYA 30.
- We know you need to SLAM, so while the sock is soaking the stabilizer, make sure the pH is lowered to about 7.2,, then increase the FC to "12". That will be your FC SLAM level until you pass all 3 SLAM criteria. Make sure to brush the pool, check the filter pressure/backwash, and most important maintain that FC of 12 as best as you can until the SLAM is complete.
- The TA is fine. CH is slightly elevated, but not much you can do. Make sure you're never adding cal-hypo shock products which increase CH quickly.
If the reagents were stored indoors in the shade or cool place, they should be okay. At least to get you through the SLAM. But at some point you know you can always go back to TFTestkits and order some refills when you're ready. Hope that helps.
Yes helps alot ! Poll math said to add 49oz of bleach, 84 oz of stabilizer ( I could only get 32 oz into the sock so I will refill after it dissolves ). PH was very high probably higher than 8.2 so I added PH Down-20oz per the label. Pool math also told me to add 184 oz of baking soda to fix TA, should I? What are cal-hypo products? I've been using bleach. Thanks Pat.
- May 3, 2014
- 58,298
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
Do not add baking soda. Manage your pH and see where it stabilizes. Better to use muriatic acid rather than powder acid. Powder acid is sodium bisulfate and the sulfate are corrosive to metal and concrete.
Cal hypo is a form of solid chlorine. Do not use. Keep using your liquid chlorine.
Cal hypo is a form of solid chlorine. Do not use. Keep using your liquid chlorine.
Have you tested your water for Phosphates? I realize I am a new guy here but it is a simple test and something I test for when Black algae shows up.
PH settled at 7.2. Its an above ground pool so no metal or concrete. Will keep using the liquid chlorine and try to get FC up to 12 today.. Thanks !
- - - Updated - - -
Phosphates? How would I test for that?!
- Jun 22, 2014
- 47,752
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
No need to worry about phosphates. Phosphates can feed algae, but when a pool is algae-free, the phosphate count is irrelevant. It's typically a number provided by pool stores who in-turn attempt to sell products like Phos-Free that do more to reduce your checking account than algae count. Maintain the proper FC level and you'll do just fine.
In my area we have a high phosphate level with water added, dust from fertilized fields and pollen. If the FC gets low the phosphates take over and you can dump all the chlorine in you want and it feeds the phosphates and the phosphates in turn let the black algae grow since your FC is inert because of the phosphates locking it up.
Treat the problem and the solution is simple.
In the presence of chlorine, phosphates become inconsequential. Phosphates are a nutrient/food source for algae and plants (hence the use in fertilizer). Int the absence of chlorine, phosphates provide the food for algae to rapidly grow. There is no such thing as the chlorine becoming inert, it is simply used up. The inability to hold a chlorine residual is tied to the CYA levels and not the phosphate levels. In this case the lack of CYA is preventing the chlorine from doing it's job because the chlorine is burned off by the sun as soon as it is added. You could make the argument that you are controlling algae by limiting the food source (phosphate), however, the key word is controlling, you are not eliminating the algae but merely controlling it. Much easier to maintain proper CYA/chlorine levels, kill the algae, and be done with it.
Makes sense to me. Current readings: FC 8, CC 0 TA 100, CYA 20. Added a little more stabilizer today and 1/2 gallon of chlorine this morning and 1/2 this evening to try to keep it at 12 shock level. Water is crystal clear but still have the little squiggly marks on the button. Swept the pool this morning and vacuumed late this afternoon. Running the pump 24/7.
I know that once phosphate levels are above 200 ppb that the algae becomes resistant to chlorine. Becoming inert might not have been the right phrase but it is the easiest for someone to understand. Just Google phosphates vs chlorine in a swimming pool.
Dave, just be careful adding too much CYA, it takes a while to dissolve and show on the test, it is better to slowly creep up on your target than overshoot it. It sounds like you are winning the battle, keep the FC up and you will be amazed at the clarity of your water.
Siber, can you please share your knowledge on how you know algae becomes resistant to chlorine once phosphates reach 200ppb? I just did a quick google search and the first two links I viewed did not support your statements. I would love some links to proven, substantiated and accredited information.
Siber, can you please share your knowledge on how you know algae becomes resistant to chlorine once phosphates reach 200ppb? I just did a quick google search and the first two links I viewed did not support your statements. I would love some links to proven, substantiated and accredited information.
I clean and service pools in East Tennessee as well as work for a Builder, I have been working around pools for 40 years in construction as well as service and maintenance.
Now besides actual fighting Phosphates in 2 to 3 pools a year that are running FC 3 to 4, TA of 100-125, CYA levels at 50 and PH at 7.0 -7.2 and one of those is a sub division pool that sees regular inspections by the health department and you come in on your weekly visit and the black algae is growing, phosphate levels are 200-250 PPB. Treat the problem and get rid of the phosphates and the algae stops growing and goes away
I left the name of the product out since I am not advertising any thing. Orthophosphates are what Phosphates turn into and is used by the Algae as food.
http://www.poolsupplyworld.com/blog/what-are-phosphates-and-how-do-they-affect-your-swimming-pool/
This explains what phosphates do to chlorine
http://blog.orendatech.com/phosphates-affect-chlorine-efficiency
Now I realize I am the new guy, I have learned stuff from your site and have it saved on Taptalk, hence the reason this came as one of the suggestions.
- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
You are mistaken and so is that blog post (ie, not a scientific peer-reviewed paper).
Basically that Orenda Blog post is horribly misinformed on how buffer chemistry works or their chemists tried to explain it to the marketing guys but then the marketing guys changed it so they could more easily justify selling a product. The one chemical equation they actually write out is the basic chlorine dissociation equation and then the equilibrium equation between hypochlorous acid (HOCl) and hypochlorite (OCl-). They then state that phosphates interfere with the equilibrium of HOCl/OCl- by causing the reaction to shift toward hypochlorite (OCl-). Great little equation but they leave out some HUGE details. For one, there isn't enough phosphate (PO4) around to have any appreciable buffering effect as your are talking about part per billion levels is most pools (somewhere around 50-100 micro-molar concentration). At those concentrations the carbonate buffering species and cyanurate buffering species are 100X times more concentrated and much more effective at holding pool water pH to a specific value. Phosphates are simply irrelevant as a hydrogen ion consuming species and will have no practical effect on the HOCl/OCl- equilibrium. Also, that blog post gets the entire notion of buffering wrong - the pH of the solution is determined by the concentration of all alkaline species in the water, both permanent and temporary forms. The pH is what it is at any given moment and so the equilibrium concentration of HOCl/OCl- is set no matter what chemical species are actually contributing to the buffering of the water volume. Because phosphates do not directly react with chlorine, then it's pointless to consider their role in hydrogen ion concentration changes because they simply do not matter. If phosphates reacted directly with chlorine, then there would be some appreciable change in pH in a manner that is similar to how the outgassing of CO2 causes the pH to shift. But, that is simply not the case - chlorine and phosphates do not react with one another. Finally, there are some very technical details about the ionic strength of pool water (caused mostly from the presence of salt) that shifts the pK2 value of phosphates in water to values much lower than normal pH levels found in pool water (the pK2 of phosphates can easily drop below 7.0 when salt is present in water). This drop in pK2 means that the peak buffering levels of the phosphate ions will be far away from the pH of water thus rendering the buffering capacity of phosphates to very low levels.
As for why you see a difference when phosphate removers are added, that's easy. Phosphates are algae nutrients (along with nitrates and dissolved carbon species). If you remove nutrients from the water volume, you make it harder for algae to regrow once it has been sanitized by chlorine. Black algae is more prevalent in your part of the country and will typically grow in pools where there is limited sunlight (shaded walls) and low chlorine levels. Maintenance companies and uninvolved pool owners typically do not keep appropriate FC levels in pools and so there is much more of a chance of the active chlorine levels falling well below the concentrations needed to keep algae at bay. Black algae is a very persistent nuisance to pools because it grows in spots and grows into the pool surface with root-like structures. Black algae also develops a fairly thick hydrophobic coating on its surface making it highly resistant to chlorine exposure. Normally one needs to treat black algae with SLAM levels of chlorine and lots of vigorous brushing to ensure that chlorine makes it to the surface of the algae. Stainless steel brushes are often needed on plaster pools to help break up the algae's protective coating. Finally, after the algae is visually cleared away, the pool owner needs to increase the FC to an elevated shock level for 24 hours to ensure that all of the algae "root" is killed. Very often it is the case that pool owners with persistent black algae problems simply need to maintain higher baseline levels of FC to avoid regrowth as the chlorine slowly attacks the algae deep in the pool wall surface. Supplemental algaecides like polyquat-60 can and should be used to help hold the algae growth at bay. One can certainly use phosphate removal treatments to reduce algae nutrients and make it harder for the algae to regrow.
My suggestion to you is that if you are truly interested in learning the science and chemistry of what we teach, you do a more thorough job of reading through what is taught here. Richard Falk (aka, chem geek) has written most of the definitive threads on pool water chemistry on this forum and other pool & spa forums as well. He has worked with and contributed to much of the current recreational pool water standards set by industry trade groups and the EPA over the last 10 years. While a lot of what he has written falls on deaf ears because it is not simple or profitable, truth is not dependent on what people want to hear, it is simply truth. I'll leave you with Richard's thread on advanced pool water chemistry and you can bookmark that and read it at your leisure -
Pool Water Chemistry
Yes Bill, I have been careful with the CYA. Its staying right around 20. The stabilizer dissolved quickly and I have added a little twice and tested several times-still 20. Chlorine is still being used but its staying high longer and not dumping 1-2 gallons of bleach in per day the way I was before. Brushing, vacuuming every day but black squiggly lines keep coming back ! At this point I don't know what to do.Any advice?
Although I am in the Minority here and no matter what I say it is not going to change anyone else's mind. Get a phosphate test kit or have your local pool store test it for Phosphates. Treating the problem is needed, since obviously treating the symptoms isn't.
You can tell the guy who wants to loose weight to walk a mile a day. But not changing his diet it is going to take a long time
You can tell the guy who wants to loose weight to walk a mile a day. But not changing his diet it is going to take a long time
- Jun 22, 2014
- 47,752
- Pool Size
- 17888
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Dave, I always remind folks to try and keep the SLAM process simple. For example, you say the CYA is around 20, but here at TFP that's not accurate because we know the vial doesn't read anything below 30. From extensive testing last season, we know that once the granules fully dissolve, the CYA registers in about 24 hours. So make sure you have at least a CYA of 30, that way you know your FC of 12 matches. If you end-up hitting a CYA of 40, the SLAM FC level will be 16, so it's not a huge difference. Once you pass all 3 SLAM criteria to resolve any standard algae concerns, that's when we might recommend taking your FC up to a Mustard Algae-type level, but only for about 24 hrs. That might help attack those stubborn spots better. After that, you might find that your pool needs a slightly elevated FC level for a few weeks to penetrate those spots. BUt for now, focus on the simple tasks for the regular SLAM.
Hi Pat,
The 20 reading is right at the top of the vial. I'm a little short of that say 22. I will continue to add stabilizer a little at a time to inch CYA up. Added a 1/2 gallon of bleach too. What is mustard type algae level?
By the way I got my TF-100 replacement kit and am using it now.. Also I should mention the black spots are not as widespread as before? As we making progress? I sure hope so!
The 20 reading is right at the top of the vial. I'm a little short of that say 22. I will continue to add stabilizer a little at a time to inch CYA up. Added a 1/2 gallon of bleach too. What is mustard type algae level?
By the way I got my TF-100 replacement kit and am using it now.. Also I should mention the black spots are not as widespread as before? As we making progress? I sure hope so!