Cyanuric Acid PPM Drop and Iron

[smallpooldad]

Waterbear,

Thank you for your reply.

Actually the difference, for my pool, is between 0.21 and 0.34 is 0.13. You might have been reading to quickly before you popped off your reply. This difference has been kindly rectified by JasonLion with his borate adjustment. I am not sure if the difference is logarithmic, if it is then it could be important, but as the error has been fixed this is a mute point and would therefore not have solicited my question.

As I at present cannot afford to send my water to be tested at a chemical laboratory. I will have to put my trust into the arms of Taylor test kits, as do many others.

I am trying to achieve and approximate CSI value of around -0.20, and difference 0.05 either side of that number would of course be acceptable, as my water fluctuates anywhere from 78 F to 86 F, with 82 F or 83 F being the norm.

This approximate figure of -0.20 seems, from all I have read, to be a good place to aim. The inaccuracy of tests is something we all sadly will have to live with. I think most of us who have been testing for a while know that, but your comments might help others who are unaware that they are not that accurate; although JasonLion with his correction to the "Pool Calculator" has rectified this CSI anomaly.

Aloha.

 

[chem geek]

Just so you know, there was a user in the industry on this forum who believed that corrosion would occur below an index of 0.0, though it would take a decade of more. His point was that a long-term negative saturation index could reduce plaster life from 30 years to 20 or 10.

The -0.2 target came from minimizing scaling possibility in a gas heater that is at higher temperature and in an SWG cell (and in The Liquidator). Technically, if you are closer to 0.0 and don't find scaling problems, then that would be potentially slower dissolving of plaster/gunite/grout, BUT as waterbear points out there are many sources of error and though extremes are easy to see in terms of problems, we don't know what happens definitively by being a little away from 0.0. The scale IS logarithmic, but even though a difference of 0.3 is a factor of 2 difference in the product of two concentrations, we don't know what this translates to in real dissolving rates. If pool plaster were really dissolving relatively quickly, you'd see an increase in pH, TA and CH over time (assuming no competing factors lowering these parameters).

Finally, corrections made to the saturation index by Wojtowicz have it be around 0.11 to 0.14 higher depending on temperature and salt level. I have his corrections turned off by default in the spreadsheet (they are at lines 222 to 224) as the spreadsheet was designed before I ran into his info and the spreadsheet closely matches the Taylor watergram.

I'm just giving you this info so you know that this isn't exact science here even if the measurements were more precise.

Richard

 

[Guest]

I'm just giving you this info so you know that this isn't exact science here even if the measurements were more precise.

Richard

Exactly the point I keep stressing!!!!!!
It's a swimming pool for goodness sake, not a chemistry lab. People need to spend less time stressing about the 'chemistry' and more time enjoying the water!

 

[smallpooldad]

Chem Geek,

Thank you for the info. Well at a calculated -0.20 (at worse case), with Wojtowicz's adjustment of 0.11 to 0.14 higher, depending on temperature and salt level, it would be still be slightly negative, most probably.

My numbers are pretty much the same as the pool school for SWG, except for Calcium, but we have a feeder; and there never seems to be any build-up on the salt cell, so all is well.

One question I do have is do you have an SWG and if so do you keep your CyA at 30-40 ppm, or do you use the 60 - 80 ppm method? If you do use the the 30 ppm method why do you do that?

Aloha.

 

[smallpooldad]

Waterbear,

My secondary question was to do with CSI adjustment and on this Chem Geek has made it very clear as to its strengths and lack thereof.

We are all different, some like to be broad in their numbers, others like to me more precise. This is human nature, it does not mean that one is right and one is wrong, but just where one feels more comfortable. So please do not stress over my questions. I am far too old to think I am right.

If I wish to treat my pool as a chemistry experiment so be it. Frankly, this would be a rather boring experiment, and I do swim in it nearly every day that I am at home, so I do enjoy the water.

Edited for being off topic. JasonLion

I know you are only trying to help, and your many posts are very helpful. Please let others be what they want to be, if they want to play chemistry lessons with their pool, and they enjoy it, let them be.

Using fewer, or no, exclamation marks would make your last reply, all the more appealing and less aggressive sounding.

Edited for being off topic. JasonLion

Aloha.

 

[chem geek]

One question I do have is do you have an SWG and if so do you keep your CyA at 30-40 ppm, or do you use the 60 - 80 ppm method? If you do use the the 30 ppm method why do you do that?

I don't have an SWG and I have an opaque pool cover so that's why I tend to keep the CYA lower since the exposure to sunlight is only 1-2 hours per day. However, I plan to go a little higher this next season to around 40 ppm or maybe even 50 ppm (with a somewhat higher FC) just so the swing in FC doesn't have as much of an effect on "active" chlorine concentration. I only add chlorine about twice a week. Current loss rate is around 1 ppm FC per day (pool temp is 88F). We'll see if that drops a little at the higher CYA level. The 10 ppm CYA loss over around 5 months implies an FC loss of around 0.17 ppm per day from oxidation of CYA so the bulk of daily loss is probably from the 1-2 hours of sunlight and the rest from oxidation of miscellaneous stuff in the pool.

 

[Guest]

I stand by what I said. You are missing the point at how imprecise the measurements you are making are and therefore the validity of your calculations, also. Chemgeek understands but then again this is standard scientific procedure that he has studied, as have I. You are stressing over result differences that are overshadowed by the margin of error in your measurements so they actually become moot!

Edited for being off topic. JasonLion

 

[JasonLion]

I am trying to achieve and approximate CSI value of around -0.20, and difference 0.05 either side of that number would of course be acceptable, as my water fluctuates anywhere from 78 F to 86 F, with 82 F or 83 F being the norm.

It is important to understand just how imprecise the test results are. The TA and CH tests are +-10 when done in the normal way, CYA is +-15, PH +-0.1, and so on. That means that your calculated CSI value is +-0.15 at best, and quite possibly even less precise than that. So saying that you want to maintain your CSI within 0.05 of some value using a standard test kit doesn't really make any sense. Day to day test variations can easily be larger than that even if nothing about your water actually changes.

Speaking as a moderator for a moment: Please try to stay on the topic of swimming pools and swimming pool chemistry/equipment/management/etc. If you have a problem with someone's posts you are welcome to bring that up with a moderator or SeanB via private message or by flagging a post as inappropriate. This forum is not the place to discuss writing style or make historical comparisons.

Chemistry experiment levels of detail are often appropriate here in The Deep End, but not elsewhere at the site. However, you may need to explain why you are interested in that level of detail or what you are trying to achieve by it and it must still be relevant to the "normal" usage of swimming pools in some way.

 

[smallpooldad]

Thank you for your responses.

Last week moved the CyA to 70 (at least I think it is 70 - see below), and raised the FC to 4.6, it was 30 and 3.6 previous to this change

The results have been as follows:

1. The SWG generator had to be turned up slightly from 16% to 20% maybe a larger chlorine FC number suffers from larger percentage losses, although this is purely speculaton.
2. The acid usage actually rose slightly, so it is not holding the pH as well, this with fractionally more shade on the pool; as the sun is lower each day until Hoku, the winter solstice, on December 21st at 2:04am. This might change over the next month or so and might be related to the new balance.

Obviously the above two are mildly negative results when compared to the previous results.

The advantage that I see is that if the CyA drops, especially if we were ever away for a few weeks it would not create a great a potential for algae development. This is a major plus.

As regards the assertion that larger CyA levels produce better results, I am agnostic on this issue. It could be, as is the case of some registry fixes in Microsoft Windows, that while it does no harm it has some minor pluses and some minor minuses. Some studies have stated that higher CyA numbers shorten the life of plaster pools although this does not seem to be proven, as not enough studies have been made.

My preference then would be to keep it at CyA 30, FC 3.6 if I knew I was not going to travel and be with my pool every week. If I used a pool person, or was not that attentive to our pool, I would go with a CyA of 70 and FC of 4.5 - 5.0.

On a lighter note, regarding my new CSI measurement I calculate it to be -0.2045689005, and I am really concerned about the final numbers starting at 456, but am working hard to resolve the issue, however I think I might have to send my water to be tested at the Lawrence Livermore National Lab just to make sure. I wonder if they take Visa and Chem Geek do you get a discount?

So as they say where I come from, the debate as to high or low CyA seems to be "A Storm in a Tea Cup", and hope now to sail in calmer waters.

Finally I would agree with Waterbear that test results are entirely subjective, see here under:

cya-testing-age-and-eye-sight-t10048.html


Aloha.

 

[chem geek]

You need to have full sun on the pool in order to see the extra chlorine protection and ability to lower the SWG on-time. Mark's tests as well as the other pools where this benefit was seen all had full sun. Since the CYA benefit is directly related to it's protection of chlorine from breakdown from sunlight, any pool that wasn't in full sun, especially when it is high in the sky (i.e. summer, if in northern latitudes), may not see the benefit. If the pool is one where CYA degradation is happening (for whatever reason) as with your pool, and it's not in full sun, then the higher CYA won't be seen to be better and could be worse.

Also, your test would actually show even worse results than you reported since the FC/CYA ratio would be made the same so a 3 ppm FC with 30 ppm CYA would scale up to around 7 ppm FC with 70 ppm CYA. That's what made the result so amazing in Mark's experiment and in the many pools where having a higher CYA, even with proportionately higher FC, resulted in a lower absolute FC loss. Mark also showed that this effect had nothing to do with the SWG itself though I do not know for certain if the effect is due to CYA's shielding effect of UV below shallow depths.

It is possible that the surface water may need to be somewhat undisturbed for the effect to occur -- basically to have a top layer depleted of some chlorine, but to have CYA shielding lower depths of UV. This is speculation on my part, but perhaps better surface circulation may lessen the effect as would occur with returns pointed more upward or from a waterfall.

If you want, you can repeat the experiment in the summertime in a pool or with large bucket or basin tests that are exposed to full sun. If you still get different results AND you see FC losses even from a covered pool or bucket (i.e. no UV) then the CYA degradation effect with your water may overwhelm the CYA sun protection benefit.

Richard

 

[smallpooldad]

Thank you for your replies.

My results could be due to the pool being covered and as you mentioned more shade in the winter.

My friend's pool which we tested after my post yesterday, his is uncovered, did see a a slight increase in FC so we turned down the SWG. There was however a large increase in pH which he said he had been fighting all week, the pH increase could be due to colder water and winds in the winter.

So all in all a mixed bag but not bad results nonetheless.

Aloha.

 

[JasonLion]

From what I saw on the other thread, it is likely that your CYA level was far below 70. If the actual CYA level was below 50, the higher SWG percentage would have been required simply because of the higher target FC level.

The increased acid demand is because you turned up the percentage on the SWG. The more the SWG runs the more the PH will shift.

The design of the plaster damage study was flawed and a subsequent study by a different group showed no effect on plaster from high CYA levels. Also, they were testing CYA levels far higher than what we recommend.

Seasonal shifts in solar illumination have very little impact over the course of a week or two, though they can be significant from one end of the season to the other.

If the pool is covered most of the time, the CYA level will be much less important. CYA protects chlorine from sunlight. If there isn't any sunlight there isn't any point in having CYA much above 20. If there is only occasional sunlight then some intermediate level may be best.

 

[smallpooldad]

Jason Lion,

Thank you for your response. The other thread was actually done at my friend's pool before we raised the CyA, so was not relative at least in it's results to these threads. I can see how that could be confusing, so please accept my apologies.

The SWG was turned up in my covered pool by 4%, my friend's uncovered pool was turned down by 2%, but interestingly he is the one stuggling with pH more than he did when the CyA was at 30. I get full sun after 1pm, he gets full sun until 1pm, in the winter. In the summer we get full sun most of the day as it is so high in the sky at our latitude. Maybe the fact that his pool is uncovered and is now cooler than before might be an additional reason for him fighting pH.

I think we have to wait and see after more than just a week or so to see if the water becomes more balanced.

In addition as Chem Geek stated the effect may not be as good in pools with high winds circulating over them. Not a problem for me as I cover but for my friend the trade winds at 16 mph to around 24 mph could negate the benefits of higher CyA. I never knew about the negative effects of high winds on higher CyA, so I learnt something new.

Aloha.