Why is my pool so dirty!!!

[bizbad]

I have a 15000 gallon inground, completely screened in. It is about six months old. I check the water chemistry twice a week and everything has always been perfect and still is. But, starting about two months ago, if I dont brush my pool atleast three times a week I get brownish yellowish dirt buildup stuck to the sides and bottom and every nook and cranny. It brushes right off except for one spot now on my swimout that I actually think is stained from it. I think I may sell my house before the marcite is all stained.

[chem geek]

This sounds like you may have mustard algae as that is yellowish/brown and looks like dust or dirt. Can you post your water chemistry levels (FC, CC or TC, pH, CYA, TA, CH, Temp.)? It seems to take a higher level of disinfecting chlorine to prevent mustard algae (close to the Max. FC ranges in Ben's chart (http://www.poolforum.com/pf2/showthread.php?t=365). It also takes a much higher level than the Shock levels to get rid of it. If you post your numbers, I can let you know what shock level will likely kill this stuff and what FC level you need to maintain to prevent it from returning.

[EDIT] What kind of filter do you have (cartridge, sand, DE, sand with some DE added) and how long do you run your pump each day? [END-EDIT]

Richard

[bizbad]

The "dirt" does look yellowish when I brush it you can see a yellowish almost orange cloud. I have a saltwater generator, FC 1.0 CC 0.0 PH 7.6 TA 100 CYA 70 temp right now is about 80 because I have the solar off so the ray vac cleans the bottom all day. pump runs 8 hours a day.

[Sully]

With your CYA of 70, your FC is way too low, at this level you should keep it maintained between 5-10ppm FC. Your going to have to boost your FC level up to at least 20 ppm to get rid of the mustard and keep it at 20. Along with daily brushings and keeping your filter running 24/7. Otherwise, the mustard is going to keep coming back. I fought with my pool for 2 months with mustard algae, before I got serious about getting rid of it for good.

[chem geek]

Sully is right, that your FC is way, way too low. You can try the 20 ppm FC to see if that kills the mustard/yellow algae, but users on this forum have found that this particular algae (which is chlorine resistent) takes a LOT more chlorine to kill. A couple of users needed to add enough chlorine (chlorinating liquid or bleach) to get to 1.0 ppm disinfecting chlorine (HOCl) concentration and with 70 ppm CYA that would take 47 ppm FC. Regardless of whether you target 20 or 47 ppm FC, you should lower your pH first to make the addition of chlorine more effective. You could first lower your pH to 7.2 (or even 7.0, but not lower) by adding Muriatic Acid. Then add lots and lots of chlorine. Let us know if the 20 ppm FC kills the mustard/yellow algae or not. I'm trying to keep track of the minimum level of chlorine needed to kill and prevent this form of algae.

After you've killed this algae, to prevent it from returning will likely require at least 5 ppm FC as Sully said, though in a non-SWG pool users have reported needing the equivalent of 11 ppm FC (for the 70 ppm CYA in your pool). Again, you'll have to experiment for your pool to see what level of FC will keep the mustard algae away, but it certainly will be far more than the 1 ppm FC that you had before.

Richard

[bizbad]

According to my pool company and my neighbors, and Aquarite the CYA and FC is right on the money. Why would the Saltwater generator company print incorrect water chemistry numbers?

[chem geek]

The problem is that most people in the pool industry -- stores, SWG manufacturers, even ORP controller manufacturers -- do not know or understand the relationship between CYA and FC (technical details of this relationship have been fortunately hidden away in The China Shop at this thread (http://www.poolforum.com/pf2/showthread.php?t=4236)). There HAVE been articles written about chlorine's lower effectiveness in the presence of CYA, such as this one (http://www.ppoa.org/pdfs/PrP_Cyanurics%20-%20Benefactor%20or%20Bomb.pdf) by the Professional Pool Operators of America (PPOA), but after my talking with a bunch of ORP sensor manufacturers and the manufacturer of Trichlor and Dichlor, I found that the manufacturer of Trichlor and Dichlor (Oxy -- Occidental Petroleum) was the only one with a clear knowledge and understanding of the chemistry involved based on scientific measurements made in 1973 and that were referred to on PDF page 18 (page 12 on the bottom of the page) of this EPA document (http://earth1.epa.gov/chemrtk/pubs/summaries/tricltrz/c14659rr.pdf). Even so, it seemed that I had worked out the details in a spreadsheet a little more clearly than those at Oxy had done, and in a presentation they made to the National Spa and Pool Institute (NPSI) in 2004 (NSPI appears to have gone away, at least in the U.S., and has been replaced by The Association of Pool and Spa Professionals, APSP), they (in my opinion) incorrectly used "averages" to make the point that only a minimum FC of 3 was needed in the presence of up to even 100 ppm CYA. They justified this by showing that out of a set of pools with varying FC and CYA, that the AVERAGE FC of pools with no algae was 3 or higher while the AVERAGE FC of pools with algae was below 3 and that even at 100 ppm CYA that minimum disinfection standards (i.e. 650 mV ORP) were met at 3 ppm FC. Of course, anyone who knows statistics knows that this is not the right way to get the right answer. The amount of CYA and FC varied in both sets of pools so some pools without algae had less than 3 ppm FC (and probably less than 30 ppm CYA) while others had more than 3 ppm FC (and possibly more than 30 ppm CYA). Also, just because a pool does not have algae does not mean that it COULDN'T have algae at that FC level -- the pool could have even been using a weekly algaecide. Finally, though it is true that 3 ppm FC with 100 ppm CYA is around 650 mV ORP and just sufficient for disinfection, this level of chlorine is NOT enough to prevent even run-of-the-mill green algae from developing. Of course, for the algae to ACTUALLY develop, it requires 1) the presence of algae cells (usually blown in from wind and leaves), 2) the presence of nutrients including carbonates (lots of those in the pool), nitrates and phosphates (often blown in from fertilizer) or silicates (not usually found in pools), 3) sunlight, 4) dissolved oxygen, 5) water (duh!) and 6) an absence of anything that would kill it such as sufficient levels of chlorine or an algaecide.

The bottom line is that the pool and spa industry as a whole is motivated by profit and there isn't much profit in having everyone use the cheapest store-bought chemicals (i.e. bleach, Borax, Baking Soda) and never having any problems with algae. I don't think that most pool store owners think that way, but nevertheless enough critical mass of manufacturers and some pool store owners do at least "not want to know" the truth if that would mean less profits. Of course, there really is plenty of money to be made by actually helping customers build and maintain pools and sell and repair equipment, but apparently the ability to sell even more chemicals is just too tempting. At least that is my opinion of the situtation.

By the way, do you brush the sides and bottom of your pool regularly, say weekly or every other week? I'm just curious as this seems to be another variable factor in determining the liklihood of developing algae. Apparently preventing biofilms from developing on pool surfaces may require less chlorine to kill the remaining free-floating algae.

[EDIT] I sent a detailed E-mail with many links to Goldline Controls suggesting, among other things, that they recommend a minimum FC level of 3 ppm (or even higher) with their 70-80 (where they say 80 is recommended) ppm CYA. I have also brought up other issues such as lower TA levels to reduce the rise in pH (they recommend 80-120 which is too broad a range -- should be 80-90). I also mentioned different salt cell designs with more plate area that could operate at lower CYA efficiently and referred to incidents of higher corrosion of coping/hardscape and metal (stainless steel poles in the pool and copper in heat exchangers) and possible ways of mitigating that problem or at least mentioning its possibility. These are all issues we have discussed at length in this forum (mostly in The China Shop). We'll see what they have to say. [END-EDIT]

Richard

[bizbad]

Interesting! I brush my pool once a week, since this started I have been brushing two or three times a week. I check my water chemistry twice a week. Why is it that the chlorinator asks for such high CYA and such low FC? Why couldnt I lower the CYA level? I just dont really want to run high levels of chlorine, so I can increase the chlorinator lifespan. I just checked my CYA again and it actually is closer to 60 than 70. The black dot test is a little speculative if you ask me.

[chem geek]

The reason that most SWG manufacturers want a high CYA level is that the salt cell operates more efficiently if there is higher CYA because the CYA combines with the generated hypochlorous acid (chlorine; HOCl) fast enough to keep the concentration of chlorine and dissolved chlorine gas low enough to make the generation of the chlorine gas at the plate efficient. If there were too little CYA or no CYA, then there would be a buildup of chlorine gas and hypochlorous acid near the generating plate and this would slow down the chlorine production rate (since the electrochemistry is a chemical reaction and like all reactions, they slow down when there are more "products").

Though I would personally prefer that the SWG manufacturers redesign their equipment to operate more efficiently at lower CYA levels (say, 30-40 ppm), this would probably require larger plate areas and longer cells. At any rate, you don't have much choice with your system so to operate efficiently, you should keep the CYA at the recommended level. So that just leaves the Free Chlorine (FC) level as the variable you can readily control and it is easy to simply set the chlorinator to run longer or at higher power (I would prefer running longer at lower power, if you have a choice) to get the FC to at least 3 or more depending on what is needed to keep algae at bay in your pool. The best way to increase your chlorinator lifespan is to run with the recommended level of CYA so that it operates at the highest efficiency. The higher FC level isn't going to burn out your chlorinator that much faster and besides, you don't have any choice since you must have that FC level to prevent algae. Yes, you could experiment and lower your CYA level and have a lower FC level to match (say, 30 ppm CYA with 1.5 ppm FC or more) and see if you can generate this at an overall lower time/power level on your chlorinator, but I bet that you will find that the chlorinator has to run a really long time to generate even a small amount of chlorine when the CYA is low (30-40 ppm).

The SWG users on this forum have found that the efficiency of the SWG is not linear with respect to CYA. In other words, at 60 ppm you aren't twice as efficient as 30 ppm and there may be a large jump from 60 to 70 to 80 ppm in efficiency. Unfortunately with CYA, it isn't easy to experiment with. You can increase it without too much trouble, but decreasing CYA requires drain and refill of part of your pool water. More technical info about the requirement for CYA in an SWG pool may be found at this thread. (http://www.poolforum.com/pf2/showthread.php?t=4495) It might be best for you to get to 80 ppm CYA and see if there is a large efficiency jump and then stay there and adjust FC higher instead (and read on for more ways to reduce chlorine consumption and therefore reduce your chlorinator's output and "on" time).

If you want to minimize the output of your SWG, then one thing you can do is to add a weekly maintenance dose of algaecide which will help stop the algae and will reduce chlorine consumption. In fact, with your algae, your SWG is working harder to even maintain 1 ppm FC so you may be partly fooled into thinking that it will need to work that hard after your algae is gone and with higher FC -- it may actually not need to be on as long (it's hard to know for sure). The best algaecide to use would be PolyQuat 60%, but weekly maintenance will get expensive. Another alternative that some users of this forum have found to be very useful (and is only a one-time cost) is to add 50 ppm Borates (measured as ppm Boron) which can be obtained from Borax (sodium tetraborate decahydrate). This is not only an algaecide and will cut down your chlorine consumption, but is also a pH buffer and will let you lower your TA to around 90 which will also help reduce the rise in pH (so you'll need to add less acid on a regular basis). Be aware that Borax is a base/alkaline so you'll be adding acid along with it, at least when initially adding it to the pool. You can find more about using Borax at this thread (http://www.poolforum.com/pf2/showthread.php?t=4712).

Richard

[bizbad]

That is interesting about the Borax. PH creep has always been a pain to me. I add a quart of acid a week to keep my ph down. The algecide benefit would be a tremendous bonus.

[Charrua2]

[EDIT] I sent a detailed E-mail with many links to Goldline Controls suggesting, among other things, that they recommend a minimum FC level of 3 ppm (or even higher) with their 70-80 (where they say 80 is recommended) ppm CYA. I have also brought up other issues such as lower TA levels to reduce the rise in pH (they recommend 80-120 which is too broad a range -- should be 80-90). I also mentioned different salt cell designs with more plate area that could operate at lower CYA efficiently and referred to incidents of higher corrosion of coping/hardscape and metal (stainless steel poles in the pool and copper in heat exchangers) and possible ways of mitigating that problem or at least mentioning its possibility. These are all issues we have discussed at length in this forum (mostly in The China Shop). We'll see what they have to say. [END-EDIT]

Richard


Richard,

A quick question since I struggled this year with PH continuously sliding up after having incorrectly assumed that I could avoid this by raising the TA to 120 (prior to reading your comments that lower TA could reduce this upward movement in PH). I can only find where you clearly state that it is not a problem to lower your TA to even 50-60 for a liner pool. I have a gunite/plaster pool and was wondering whether it is also safe to have TA at those low levels. Thanks.

Alex

[bizbad]

Just wanted to report in. I chose to raise the clorine level to 35 ppm for 60 hours with pump running. I brushed each day. It has been two days since I stopped brushing and it still looks good. If I dont need to brush tomorrow I will know that I have won the battle. I am going to add Borax to the pool next week to see if I can level off the acid usage and provide some algecide benefits as well. I hope it works! Thanks for help.

[chem geek]

Just wanted to report in. I chose to raise the clorine level to 35 ppm for 60 hours with pump running. I brushed each day. It has been two days since I stopped brushing and it still looks good. If I dont need to brush tomorrow I will know that I have won the battle. I am going to add Borax to the pool next week to see if I can level off the acid usage and provide some algecide benefits as well. I hope it works! Thanks for help.
Great news about your pool getting cleared! You'll know that you've gotten all the algae if your FC level holds up overnight (or not in sunlight) and you have no (or < 0.5 ppm) CC. The 35 ppm probably worked because you started out at a little lower pH and, most importantly, the temperatures are cooler now so the algae isn't growing as fast. At any rate, it's good to know.

Don't forget to lower your TA to 90 or even 80 as that will also help. Follow the procedure at this post (http://www.poolforum.com/pf2/showthread.php?t=191) to lower your TA.

Your biggest problem now will be how to get your FC level back down if there isn't any sun to break it down, but technically with a CYA of 70 ppm and an FC of 35 ppm, the disinfecting (and oxidizing) chlorine level is at the same level as it would be if you had 1.0 ppm FC with no CYA. Though I would be confident enough to actually swim in such water, I'm a nutty chem geek. There's always the possibility that the chlorine bound to CYA does something nasty we don't know about (though it doesn't show up in ORP sensors, doesn't seem to kill any bugs, doesn't seem to oxidize anything, or do anything else that is detectable...). I did find that one can use hydrogen peroxide to lower chlorine levels rather than using sodium thiosulfate, so that was good news.

Richard

[chem geek]

Richard,

A quick question since I struggled this year with PH continuously sliding up after having incorrectly assumed that I could avoid this by raising the TA to 120 (prior to reading your comments that lower TA could reduce this upward movement in PH). I can only find where you clearly state that it is not a problem to lower your TA to even 50-60 for a liner pool. I have a gunite/plaster pool and was wondering whether it is also safe to have TA at those low levels. Thanks.

Alex
Alex,

If you lower your TA, then you make the water more corrosive in terms of gunite/plaster/grout so you would need to compensate by increasing Calcium Hardness (CH) or keeping the pH higher or both. However, you generally don't run into problems with corrosion (or scaling, in the other direction) until the saturation index is quite a bit out of whack. Nevertheless, if you post a full set of numbers, especially for your pH, CH, CYA, salt level or TDS, current TA, and temperature, then I can give you an idea of where you are currently at and what you can do after lowering the TA.

Richard

[Charrua2]

Alex,

If you lower your TA, then you make the water more corrosive in terms of gunite/plaster/grout so you would need to compensate by increasing Calcium Hardness (CH) or keeping the pH higher or both. However, you generally don't run into problems with corrosion (or scaling, in the other direction) until the saturation index is quite a bit out of whack. Nevertheless, if you post a full set of numbers, especially for your pH, CH, CYA, salt level or TDS, current TA, and temperature, then I can give you an idea of where you are currently at and what you can do after lowering the TA.

Richard

Thanks Richard,

Haven't tested the water since I closed it but I can tell you that the numbers usually were as follows:

FC = 2-5 (I rarely shock)
CC = 0
CYA = 40
Salt level or TDS = ? (never tested for this)
TA = 100 - 120 (used to be 90 and I raised it to 120...After that it lowers when I add the acid but then creeps up)
PH = 7.6 - 8.0 (added acid once a week...PH always creeped up but the upswing was quicker after I increased the TA)
CH = 350
Water temp = 75-90 degrees depending on month

Other info that might be of use: I only use bleach and I don't have a heater.

Thanks again

[chem geek]

Charrura2,

In your situation, you can lower your TA to 80 or even 70 with absolutely no problems (even if you did have a heater, which you don't). You can do that (following the procedure at this post (http://www.poolforum.com/pf2/showthread.php?t=191)) when the temps come back up since trying to lower your TA when temps are low can be more difficult. The lower TA will definitely help your battle of rising pH and you should be able to keep your pH around 7.5 without too much difficulty. Your CH is already elevated at 350 and helps compensate for the lower TA that I am proposing so your water will be in near perfect balance at the lower TA levels (currently, your water is over-saturated with calcium carbonate, but not so much as to cause cloudiness or scaling).

Richard

[Charrua2]

Charrura2,

In your situation, you can lower your TA to 80 or even 70 with absolutely no problems (even if you did have a heater, which you don't). You can do that (following the procedure at this post (http://www.poolforum.com/pf2/showthread.php?t=191)) when the temps come back up since trying to lower your TA when temps are low can be more difficult. The lower TA will definitely help your battle of rising pH and you should be able to keep your pH around 7.5 without too much difficulty. Your CH is already elevated at 350 and helps compensate for the lower TA that I am proposing so your water will be in near perfect balance at the lower TA levels (currently, your water is over-saturated with calcium carbonate, but not so much as to cause cloudiness or scaling).

Richard

Thanks Richard,

I had read in another post where someone even lowered there TA to 50 to really fight the rising PH. Next summer, if I see that TA of 70 still doesn't do the trick, can I try lower or should I avoid the risk?

Promise this is the last question.

Thanks again

Alex

[chem geek]

Remember that TA is composed of all alkalinity, both carbonate alkalinity and the alkalinity from CYA (and other lesser components) so even 70 ppm TA is risky if the CYA is high (i.e. 70-80) while at a lower CYA of 30 ppm then 70 ppm is OK. A 50 ppm TA even with a low CYA of 30 ppm, is on the corrosive side (not terribly -- just my being picky), and though this can be mitigated by running a higher CH and a higher pH, I would only do that if the rising pH was a really bad problem. At 50 ppm TA, a CH of 400 and a pH of 7.6 (instead of 7.5) would be better.

Richard

[Charrua2]

Remember that TA is composed of all alkalinity, both carbonate alkalinity and the alkalinity from CYA (and other lesser components) so even 70 ppm TA is risky if the CYA is high (i.e. 70-80) while at a lower CYA of 30 ppm then 70 ppm is OK. A 50 ppm TA even with a low CYA of 30 ppm, is on the corrosive side (not terribly -- just my being picky), and though this can be mitigated by running a higher CH and a higher pH, I would only do that if the rising pH was a really bad problem. At 50 ppm TA, a CH of 400 and a pH of 7.6 (instead of 7.5) would be better.

Richard

Ok, so it looks like if I go the route of lowering the TA to 70, I will have to keep on top of the CH a bit more than in the past. It's something I used to test once a month since it never really seemed to move way out of wack (ie, always between 300-400).

We'll see how it goes next year. Thanks once again.

[Charrua2]

Remember that TA is composed of all alkalinity, both carbonate alkalinity and the alkalinity from CYA (and other lesser components) so even 70 ppm TA is risky if the CYA is high (i.e. 70-80) while at a lower CYA of 30 ppm then 70 ppm is OK. A 50 ppm TA even with a low CYA of 30 ppm, is on the corrosive side (not terribly -- just my being picky), and though this can be mitigated by running a higher CH and a higher pH, I would only do that if the rising pH was a really bad problem. At 50 ppm TA, a CH of 400 and a pH of 7.6 (instead of 7.5) would be better.

Richard

Richard,

I opened my pool this season and am in the process of lowering the TA to 70 (as mentioned above). One number that changed over the winter season is the CH which is now at 175. I have purchased 8 llbs of Calcium Increaser from Walmart which should raise the CH to approx. 200. Should I raise it more or keep it there. My guess is that CYA is at appox 20 (dot never disappears completely but FC has not diminished too quickly). What do you think? As always, thank you.

Alex

[chem geek]

If you want to have your pH closer to 7.5, then I would raise your CH level to around 300 ppm. Otherwise, you could just run your pH around 7.7 at your current CH level of 175 and be fine. It's not a big deal either way -- I'm just letting you know what is closer to ideal. Having your pH target at 7.7 would result in even less rise in pH, but if you don't see much of a rise at 7.5 and want that as your target instead, then the higher CH level would be better (but not a huge problem if you didn't do it -- the saturation index at pH 7.5, CH 175, TA 70 and CYA 20 is about -0.3).

Richard