Why is my pool so dirty!!!

[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. 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). There HAVE been articles written about chlorine's lower effectiveness in the presence of CYA, such as this one 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. 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.

[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