Chemistry measurements 2 months in...

[tgmb]

We replastered the pool 31 May 11- filled that day. Installed a sand filter with zeosand, a two speed EcoPump EP-6, a Spectralight SL-500, a GE 15087 DPDT controller, and kept the RayPak 2100. Because we ripped out the old booster pump, I just switched from a Polaris 280 to a Polaris 360, which I run (on high speed) one hour a day. The pump runs at low speed the other 23 hours a day. (Filter is 3 psi at low speed-pump at low speed is 53 decibels at 3 feet.) Pipes are 1.5". The Spectralight is on 24/7.

Last week, I bit the bullet, and based on a 20k gal. pool, I put in 16 boxes of mule team borax and 5 gallons of 20 baume.

(I noticed something; I did it in two phases, 8 boxes, 2.5 gallons, adjusting pH afterwards. After the first phase, which would be about 25 ppm borax, the water felt WORSE- eyes burned. After the second phase, 50 ppm, the problem went away. What's that all about?)

This week, I put in 200 lbs of blue bag water softener salt. After I put it in, I liked the feel, so I put in another 160 lbs. The change is night and day- far better on the eyes and skin. Plus, the water appearance is more crystalline. (I was skeptical.) Adding chlorine with safeway regular bleach when I test, which has been about 3 times a week.
(I need a SWCG, but there are other priorities right now.)

That's the background.

As far as chemistry goes, my numbers this morning at 0900 are as follows: (Taylor K-2005; will get a 6 or T100 soon..)
temp- 84f.
TC-1
FC-1
CC-0
pH-7.4
TA-130
CH-450
CYA-45
CSI-.5
Borates-50 ppm

(Don't have sodium test strips yet, but should be about 2000 ppm.)

Now, according to the CYA/Chlorine chart, I'm way low on chlorine. (Minimum FC 3, goal FC 5, according to the chart.) My CH is high, but this is new plaster, so I expect that. And my CSI is at risk for scaling, although I doubt that will happen. Ideally, I'd like to get my CYA down to about 20 or so, but I'm not in a rush, as I don't see the need, and I'm dubious about the "CYA REMOVER" on sale at the local pool store. What I find interesting, is the appearance of the water under these conditions. (CAVEAT- The family is away- I am the only swimmer, 1 hour a day for the last week.) Any suggestions?

 

[JasonLion]

Why would you want to lower your CYA level? It is just about perfect where it is. CYA remover kind of works, but it gets extremely expensive and tends to make a cloudy mess of the pool. Most stores have stopped selling it because of the huge number of complaints.

I doubt that you really need to run the pump 24/7. Most likely you can run the pump significantly less than that.

If you frequently allow FC to get that low you will eventually have problems, though not necessarily for a while.

 

[Richard320]

Raise the FC. Work on lowering TA some, it will affect CSI a lot. And I would worry about scaling...I grew up in Cambrian Park and lived near Westgate and downtown Campbell for another 20 years. The water is HARD. I suspect my pool was not started correctly, and when I bought the place 2 years after replastering, it already had a lot of scale that I get to deal with. Scale is like an STD: It's easier to never let it get started than to get rid of it.

 

[tgmb]

I'd eventually like to get down to the 20/3 range, As to why-so long as the water is disinfected, why not? (Don't get me wrong- life is carcinogenic- but we should be prudent when we can...)

"Genotoxic Effects in Swimmers Exposed to Disinfection By-products in Indoor Swimming Pools
Manolis Kogevinas,1,2,3,4 Cristina M. Villanueva,1,2,3 Laia Font-Ribera,1,2,3 Danae Liviac,5 Mariona Bustamante,1,3,6 Felicidad Espinoza,5 Mark J. Nieuwenhuijsen,1,2,3 Aina Espinosa,1,2,3 Pilar Fernandez,7 David M. DeMarini,8 Joan O. Grimalt,7 Tamara Grummt,9 and Ricard Marcos3,5
1Centre for Research in Environmental Epidemiology, Barcelona, Spain; 2Municipal Institute of Medical Research, Hospital del Mar, Barcelona, Spain; 3CIBER Epidemiologia y Salud Pública, Barcelona, Spain; 4National School of Public Health, Athens, Greece; 5Grup de Mutagénesi, Departament de Genética i de Microbiologia, Universitat Autònoma de Barcelona, Bellaterra, Cerdanyola del Vallés, Spain; 6Centre for Genomic Regulation, Barcelona, Spain; 7Institute of Environmental Assessment and Water Research, Barcelona, Spain; 8National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; 9Federal Environmental Agency, Bad Elster, Germany
Background: Exposure to disinfection by-products (DBPs) in drinking water has been associated with cancer risk. A recent study (Villanueva et al. 2007; Am J Epidemiol 165:148–156) found an increased bladder cancer risk among subjects attending swimming pools relative to those not attending.
Objectives: We evaluated adults who swam in chlorinated pools to determine whether exposure to DBPs in pool water is associated with biomarkers of genotoxicity.
Methods: We collected blood, urine, and exhaled air samples from 49 nonsmoking adult volunteers before and after they swam for 40 min in an indoor chlorinated pool. We estimated associations between the concentrations of four trihalomethanes (THMs) in exhaled breath and changes in micronuclei (MN) and DNA damage (comet assay) in peripheral blood lymphocytes before and 1 hr after swimming; urine mutagenicity (Ames assay) before and 2 hr after swimming; and MN in exfoliated urothelial cells before and 2 weeks after swimming. We also estimated associations and interactions with polymorphisms in genes related to DNA repair or to DBP metabolism.
Results: After swimming, the total concentration of the four THMs in exhaled breath was seven times higher than before swimming. The change in the frequency of micronucleated lymphocytes after swimming increased in association with higher exhaled concentrations of the brominated THMs (p = 0.03 for bromodichloromethane, p = 0.05 for chlorodibromomethane, p = 0.01 for bromoform) but not chloroform. Swimming was not associated with DNA damage detectable by the comet assay. Urine mutagenicity increased significantly after swimming, in association with the higher concentration of exhaled bromoform (p = 0.004). We found no significant associations with changes in micronucleated urothelial cells.
Conclusions: Our findings support potential genotoxic effects of exposure to DBPs from swimming pools. The positive health effects gained by swimming could be increased by reducing the potential health risks of pool water.
Key words: cancer, chlorination, disinfection by-products, genetics, genotoxicity, mutagenicity, swimming pools, water. Environ Health Perspect 118:1531–1537 (2010). doi:10.1289/ehp.1001959 [Online 12 September 2010]
"

 

[tgmb]

Richard,
Tap water CH is 160- I may just backwash, refill, and rebalance.

Tom

 

[tgmb]

Jason,
As for running the pump 24/7, continuous circulation and filtration are better for the pool water. (We'll have to agree to disagree about the Spectralight aspect of things.) Plus, at low speed, the power usage is negligible (WAY down from the old pumps)- so why not?. Additionally, from a simplicity standpoint, it's a more of a steady state system- easier to work with. And my goals are safety and simplicity.

Tom

 

[chem geek]

I'd eventually like to get down to the 20/3 range, As to why-so long as the water is disinfected, why not? (Don't get me wrong- life is carcinogenic- but we should be prudent when we can...)

"Genotoxic Effects in Swimmers Exposed to Disinfection By-products in Indoor Swimming Pools"

I wrote about this study and related ones before here. Note that the studies are with indoor pools that had no CYA in them and that with 1.2 ppm FC average they had over 10 times higher active chlorine (hypochlorous acid) levels than pools where the FC is around 10% of the CYA level. Also, outdoor pools exposed to UV in sunlight and with better air circulation have lower DBPs. Finally, the amount of DBPs is a function of bather load (unless you have a lot of blown-in organics in the pool).

Your wanting a lower CYA level doesn't make sense unless your pool isn't exposed to sunlight. If exposed to sunlight, then a lower CYA level will require a lot more chlorine use (higher daily chlorine demand). Usually, a 40-50 ppm CYA target is a reasonable balance for protection of chlorine while not being too difficult to shock the pool if that ever becomes necessary. Remember that it is NOT the FC level alone that determines the amount of active chlorine (hypochlorous acid) in the water, but rather the FC/CYA ratio. Having a higher CYA with higher FC does NOT result in any more active chlorine. It is the active chlorine that oxidizes swimsuits, skin, hair, organics, etc., NOT FC alone.

If you find your pH tends to rise over time or your pool looks cloudy or you get scaling, then you can Lower Total Alkalinity. As Richard notes, you want to prevent scaling since it's a bear to remove without hurting your plaster surface. If your pH rose for any reason, the pool could start to scale. We've seen pools scale with the CSI at +0.7 and be severe at +1.0 or higher, but in spas I've read reports of scaling at +0.3 and in a gas heater the CSI is higher so scaling can occur and not be visible (but still cause damage from overheating in the heater).

 

[tgmb]

So, in light of my setup, (no pun intended), what would you recommend? Spectralight recommends .5 FC and 3-8 CYA after initial setup and baseline shock. Based on your CYA chart,
that would be suboptimal.
On a more technical note, I've read the data on CYA, and it seems pretty innocuous, from a carcinogenic standpoint. Would sequestered chlorine be the same? I'm thinking in terms of long term dermal absorption.

Thanks- your contributions have been very educational.

 

[tgmb]

Another question- wouldn't DBP generation be independent of chlorine level past a certain threshold? In other words , if X equals the amount of waste generated, wouldn't that convert to a given Y of DBPs, regardless of chlorine levels past the minimum chlorine required for full oxidation?

 

[tgmb]

As far as CSI, I just went ahead and backwashed about 3 inches and refilled. I'll retest in the am.

 

[chem geek]

So, in light of my setup, (no pun intended), what would you recommend? Spectralight recommends .5 FC and 3-8 CYA after initial setup and baseline shock. Based on your CYA chart,
that would be suboptimal.

It's pretty obvious from this page of theirs that these guys really don't know what they are talking about. Specifically, they say the following which is where I presume you got your information:

Once CYA levels reach 30 - 50, chlorine's power decreases significantly. Scientific studies have proven that CYA levels over 20 ppm provide little benefit over CYA levels of 8-10 ppm. In fact, cyanuric acid levels over 50 significantly affect chlorine's ability to do its job.

That is just pure bunk and displays their ignorance. The relationship of chlorine and Cyanuric Acid was definitively determined in 1974 as described in this paper. It is absolutely not true that chlorine's power decreases significantly only when CYA levels reach 30-50. Even 10 ppm lowers active chlorine levels significantly. As I described earlier, the active chlorine (hypochlorous acid) level is roughly proportional to the FC/CYA ratio (this is technically derived in this post). It is also untrue that CYA levels over 20 ppm provide little benefit over CYA levels of 8-10 ppm and there are many, many people on this forum who would tell you for a fact that you lose a LOT less chlorine at higher CYA level if the pool is exposed to direct sunlight and this is even true if you maintain the same active chlorine level by maintaining the same FC/CYA ratio. In fact, Mark did an experiment described in this post that showed the difference in chlorine loss between 45 ppm CYA and 80 ppm CYA. It is also untrue that CYA levels over 50 ppm prevent chlorine from doing its job -- if one raises the FC proportionately then there is no difference in active chlorine level (and consequently in ORP). That is, 1 ppm FC with 10 ppm CYA is the same as 10 ppm FC with 100 ppm CYA. This myth that levels of CYA above 20-30 don't provide any benefit comes from high bather-load commercial/public pools where the chlorine demand from bather load outweighs the loss from chlorine such that little additional savings comes from higher CYA levels, but in low bather-load residential pools this is not the case.

On a more technical note, I've read the data on CYA, and it seems pretty innocuous, from a carcinogenic standpoint. Would sequestered chlorine be the same? I'm thinking in terms of long term dermal absorption.

Dermal (skin) absorption of CYA is minimal as described in this link and this PDF file at 5 µg/kg/day. There is not specific data about the chlorinated isocyanurates in terms of skin absorption, but given that the primary species is negatively charged (HClCY^-) and looks very similar to the primary species of cyanuric acid (H₂CY^-), they likely behave the same and are not absorbed by the skin. As described in the "Chlorine/CYA Relationship" section of this post, the chlorine bound to CYA is about 1/100th as reactive an oxidizer as hypochlorous acid and it also has a very slow (if any) disinfection rate.

Another question- wouldn't DBP generation be independent of chlorine level past a certain threshold? In other words , if X equals the amount of waste generated, wouldn't that convert to a given Y of DBPs, regardless of chlorine levels past the minimum chlorine required for full oxidation?

You bring up a good point and the answer is that it depends on the organic source and whether it builds up or is not always present or is volatile and outgasses. For example, when it comes to your skin, it is only present in the water when you are in the water so both the rate and total amount of DBPs from your skin are going to be dependent on the active chlorine level. The same is also true for bather waste that produces volatile DBPs assuming they are faster in volatizing than in their rate of introduction (on average); otherwise, if they volatize too slowly or are not volatile at all then these organic precursors will build up over time. They will eventually reach a steady state with their removal either through slow oxidation, through outgassing, or through water dilution.

There is also another factor to consider. The active chlorine level can sometimes influence which chemical pathway is taken where a lower active chlorine level can result in lower rates AND total cumulative amount of the worst DBPs for some precursors. This happens with ammonia, for example, where a lower active chlorine level produces less volatile and irritating nitrogen trichloride (this is described technically in this post).

By the way, one thing that Spectralight didn't tell you is that UV can create MORE DBPs, including some THMs, than not using UV. They are good at controlling chloramines, but research by Blatchley and others has shown that medium/high-pressure UV (i.e. broad spectrum UV) creates some DBPs while possibly reducing some others (chloramines, nitrosamines). It is less likely for low-pressure UV (i.e. narrow spectrum UV) to do so. Also, medium/high-pressure UV can convert nitrate to nitrite which is then oxidized by chlorine back to nitrate so chlorine demand can increase in pools that are higher in nitrate. You can read about such differences in this link and see that Spectralight offers both types for commercial systems but I couldn't find what type they use for residential systems.

The bottom-line is that UV systems aren't usually needed in outdoor residential pools. Sunlight breaks down some chlorine into hydroxyl radicals that are powerful oxidizers and that, along with good air circulation, tends to keep such outdoor pools in good shape. Also, the CYA used in such pools has the active chlorine level be low with its advantages (though obviously that can also be done in indoor pools, but usually isn't). It is indoor pools where there is no sunlight and poor air circulation where UV systems can help keep down combined chlorine and mostly help with DBPs, but it is far from being a panacea.

 

[tgmb]

Excellent clarification. Thank you. As far as Spectralight goes, they offer both systems for residential use (SL 400 vs SL 500 and up.)http://www.Spectralightuv.com/residential-pool-uv.html