After Some CYA Advice

[Cactus345]

Hi everyone, I have just been wondering about Cy Acid and if I really need it. This is my situation. I have a $900 Bestway 6.7m Vinyl pool which has been up for about 2 months now (my first pool). The water has been testing perfectly everyday (to me) and is crystal clear and beautiful to swim in. I have a SWG that is way too big for my pool allowing me to run it at around 20-50% depending, at 3 hrs pump time per day. It is unseasonably cold here atm, around 11 C (52F) at night and 20C (68F) day temp, so the cover has been on all of the time for the last two weeks. My well water here is very good which is what I have filled my pool with, it is very soft and has a starting pH of 4.

So 7700 gallon pool, starting pH4
9kg of DOT Solubor added (probably too much)
120kg of pool salt for SWG
A little acid and sodium hydroxide to get pH right
SWG is a Zodiac Clearwater 170 gram Cl per 6 hours max output.
1600 gph sand filter run for 1 hr in the morning and 2 hours in the evening.


Pool now tests the same everyday using HACH Aquacheck 7 test strips.
T Hard zero
T Cl 1-5 usually 3 or less depending on day
Free Cl 1-3 usually around 1 or a bit more
pH 7.6 tested with Hanna pH/EC Combo model HI 98129 (constantly calibrated).
TA around 80-120
CYA zero

With the cover on atm the Free Cl was climbing so I cut the SWG back to about 20%, still 3 hrs pump time. This is our hottest months of the year usually anywhere from 30C up and sometimes 40C so as soon as it warms up again the cover will come off and I will run the SWG at about 50% to raise the amount of Cl produced to counter for the extra swimming and the sunlight. Anyone have any issues with the above so far?

Now this is my query. As I have a large SWG that can easily and cheaply produce as much Chlorine as I want, do I really need to use Cy Acid? I've read on here that I do, but I have also read that I will need to up the free Cl to 5 or so to counter the Cya. Wouldn't I just be better leaving the Cya out of the whole thing and just keep doing what I'm doing, running the free Cl at around 1 to 2? Does it really matter if the sun is going to burn some off? I can understand that if you're buying liquid chlorine everyday that you would want Cya to help protect it, but I don't think that I need it with a small pool and a large SWG?

Also I will probably cut the pump back to 2 hours per day and up the SWG % to compensate.

Sorry for the long winded question and thanks in advance for you help! Happy swimming!

 

[JohnT]

Running without CYA makes your SWCG work harder and shortens its life. Only you can decide if that is worth the tradeoff there. You also get into issues of needing to keep your FC low enough to be tolerable for bathers and their suits without CYA while having enough in there to make it through the sunniest part of the day without the chlorine dipping too low.

 

[jblizzle]

The CYA does 2 things:
1. Protect the FC from the sun ... and thus require less FC to be added every day, even if you actual FC number you maintain is higher. At this point you do not seem worried about this.

2. Buffers the harshness of the chlorine in the water. This is a big factor and suggest you consider it. This is why we recommend CYA for indoor pools even though they do not need protection from the sun. This chart show the "harshness" of the water as a function of FC and CYA level. Your suggested FC level of 2ppm with 0ppm CYA would have an active chlorine level of 0.967. But setting the CYA at 70ppm and maintaining the FC at 5ppm would have an active chlorine level of 0.029 which is 33 times less damaging to skin, hair and suits than what you are doing now.

 

[chem geek]

Just to give you a real-world perspective on this, my wife used to swim at a local community center pool during the five winter season months going 3-4 times per week. Her swimsuits would degrade (elasticity would get shot) and last only for one season and she experienced more flaky skin and damaged hair. In our own pool that she used 6-7 times per week during the seven month summer season none of these problems occurred and the swimsuits lasted for around 7 years or so.

The main difference between the two pools was that in our outdoor residential pool I had 3-6 ppm FC with 40 ppm CYA while in the indoor commercial community center pool they used no CYA and had the chlorine at 1-2 ppm FC. Even accounting for the warm 88ºF water temperature in both pools, the community center pool had an active chlorine (hypochlorous acid) level of 0.46 to 0.92 ppm FC while our residential pool had an active chlorine level of 0.06 to 0.14 ppm FC so a difference of a factor of 3 to 15. It is this difference that explains why the swimsuits lasted so much longer when using our pool with CYA and why her skin and hair were in better shape swimming in our own pool.

Cyanuric Acid (CYA) significantly moderates chlorine's strength. Without CYA, for you to have the same effect you'd have to operate your pool at around 0.1 ppm FC or less and that is simply impractical in terms of accurate measurement and not getting the chlorine used up locally by bather load or other factors. You should think of CYA as an active chlorine buffer that holds chlorine ready to be released whenever and wherever needed in the pool. It's very useful, but of course should not be overused so the FC/CYA ratio should not get too low since that determines the active chlorine level.

 

[pragmatic]

Just to give you a real-world perspective on this, my wife used to swim at a local community center pool during the five winter season months going 3-4 times per week. Her swimsuits would degrade (elasticity would get shot) and last only for one season and she experienced more flaky skin and damaged hair. In our own pool that she used 6-7 times per week during the seven month summer season none of these problems occurred and the swimsuits lasted for around 7 years or so.

The main difference between the two pools was that in our outdoor residential pool I had 3-6 ppm FC with 40 ppm CYA while in the indoor commercial community center pool they used no CYA and had the chlorine at 1-2 ppm FC. Even accounting for the warm 88ºF water temperature in both pools, the community center pool had an active chlorine (hypochlorous acid) level of 0.46 to 0.92 ppm FC while our residential pool had an active chlorine level of 0.06 to 0.14 ppm FC so a difference of a factor of 3 to 15. It is this difference that explains why the swimsuits lasted so much longer when using our pool with CYA and why her skin and hair were in better shape swimming in our own pool.

Cyanuric Acid (CYA) significantly moderates chlorine's strength. Without CYA, for you to have the same effect you'd have to operate your pool at around 0.1 ppm FC or less and that is simply impractical in terms of accurate measurement and not getting the chlorine used up locally by bather load or other factors. You should think of CYA as an active chlorine buffer that holds chlorine ready to be released whenever and wherever needed in the pool. It's very useful, but of course should not be overused so the FC/CYA ratio should not get too low since that determines the active chlorine level.

^NICE-Thank you!

 

[yabbyfarm]

Thank you Chem geek and Jblizzle. That has explained the CYA vs FC very clearly.

 

[Cactus345]

Running without CYA makes your SWCG work harder and shortens its life. Only you can decide if that is worth the tradeoff there. You also get into issues of needing to keep your FC low enough to be tolerable for bathers and their suits without CYA while having enough in there to make it through the sunniest part of the day without the chlorine dipping too low.

Thanks John, I assumed that I would be producing LESS Chlorine if not using Cya, as there wouldn't be any Cl held in reserve by the Cya, only the free stuff in the pool at 1 ppm, not 5 ppm WITH Cya (plus what the Cya was hiding), and therefore my SWG would be working less and would last longer. I've been able to keep my FC at 1ppm but I need to test it everyday and constantly adjust my SWG to suit the different weather and swimming conditions, Cya would reduce this constant testing? I run the pump for 1 hr in the morning to produce enough Cl for the day, then 2 hrs in the evening.

 

[pwrstrk]

With CYA in your water your going to have still test FC to make sure keeping adequate FC levels to prevent algae.
Think of CYA like this. Just like you put sunscreen on to protect your skin from getting sunburn, the CYA is the sunscreen for chlorine. The sun is a major component of chlorine consumption, along with bather load and organics in the water.

 

[Cactus345]

The CYA does 2 things:
1. Protect the FC from the sun ... and thus require less FC to be added every day, even if you actual FC number you maintain is higher. At this point you do not seem worried about this.

Ok, so the test strip reads the Cl that is bound by the Cya too does it, and counts it as free Cl? I guess I can't understand how without Cya I can run my pool at 1ppm free Cl but have more Chlorine in the water than a pool with Cya and 5ppm free Cl.

I'm not worried because as I said I have a huge SWG and can generate Cl as I need it virtually for free (a bit of salt).

Thanks.

- - - Updated - - -

The main difference between the two pools was that in our outdoor residential pool I had 3-6 ppm FC with 40 ppm CYA while in the indoor commercial community center pool they used no CYA and had the chlorine at 1-2 ppm FC. Even accounting for the warm 88ºF water temperature in both pools, the community center pool had an active chlorine (hypochlorous acid) level of 0.46 to 0.92 ppm FC while our residential pool had an active chlorine level of 0.06 to 0.14 ppm FC so a difference of a factor of 3 to 15. It is this difference that explains why the swimsuits lasted so much longer when using our pool with CYA and why her skin and hair were in better shape swimming in our own pool.

Cyanuric Acid (CYA) significantly moderates chlorine's strength. Without CYA, for you to have the same effect you'd have to operate your pool at around 0.1 ppm FC or less and that is simply impractical in terms of accurate measurement and not getting the chlorine used up locally by bather load or other factors. You should think of CYA as an active chlorine buffer that holds chlorine ready to be released whenever and wherever needed in the pool. It's very useful, but of course should not be overused so the FC/CYA ratio should not get too low since that determines the active chlorine level.

Awesome, thanks for that, I didn't realise that there was a ratio and that a pool with Cya felt like it had less Cl than a pool without Cya, so I should run Cya at 30-50 and Free Cl at 3-6? I will check out the calculators and see what they say.

 

[jblizzle]

You will quickly realize reading the forum that test strips are worthless. To truly take control, you need one of the recommended test kits with the FAS-DPD chlorine test.

Also read the article in Pool School about the water balance for SWG pools. We recommend the CYA be in the 70-80ppm range and the corresponding FC shown in the chart in Pool School.

 

[chem geek]

Ok, so the test strip reads the Cl that is bound by the Cya too does it, and counts it as free Cl? I guess I can't understand how without Cya I can run my pool at 1ppm free Cl but have more Chlorine in the water than a pool with Cya and 5ppm free Cl.

Chlorine tests measure both the active chlorine and the chlorine bound to CYA because as the active chlorine reacts with the dye in the test half the chlorine bound to CYA is released every 0.25 seconds so is all measured in the time of the Free Chlorine (FC) test.

However, the test is essentially measuring the chlorine reserve or capacity, not its capability to prevent algae, kill bacteria, oxidize swimsuits, skin and hair, or oxidize bather waste. The unbound chlorine is active while that bound to CYA is not (technically it's around 1/150th as active for oxidation; less so for disinfection).

This post goes into more details on the concept but think of soldiers in a war fighting on the front lines having rifles while there are many, many more soldiers in reserve that are not actively shooting at the enemy. The chlorine bound to CYA is like that reserve. The total number of active and reserve soldiers tells you how long you will be able to fight in spite of losses, but it does not tell you how quickly you can kill the enemy. That depends solely on the number of active soldiers shooting at the enemy, even if an active soldier gets killed and is immediately replaced with one from the reserve.

You wouldn't be having any of this confusion if the chlorine test kit were to test only the active chlorine level, but it doesn't. Since the amount of active chlorine is roughly proportional to the FC/CYA ratio, we put together a Chlorine / CYA Chart in the Pool School that shows the minimum levels of FC for every CYA level in order to prevent green and black algae growth.

As for how much chlorine is lost to sunlight, the active chlorine that is unbound to CYA reacts quickly with sunlight where roughly half is lost every hour with noontime sun at pH 7.5 in an average pool. The chlorine bound to CYA reacts far more slowly so the net result is that the chlorine lasts longer with more CYA in the water even keeping the active chlorine level (FC/CYA ratio) constant. In most pools with CYA, the 24-hour chlorine loss is around 2 ppm FC, but in a pool with no CYA with 1 ppm FC as you describe you would lose 0.5 ppm FC every hour. Your pool is 7700 gallons so 0.5 ppm FC is 14.6 grams needed per hour so that's a saltwater chlorine generator (SWG) rated at 0.35 kg or 0.77 pounds per 24 hours to just barely keep up with chlorine loss during the day and that assumes no additional demand from bathers or other sources. Your SWG is 170 grams per 6 hours so roughly twice the output as the chlorine loss from sunlight alone. Every bather-hour in the pool requires another 4 grams of chlorine so 3-4 people in the pool for an hour could double the chlorine amount required so would be at the limit of what your SWG could produce to keep up.

So technically you could output enough from your SWG in normal circumstances (without those 3-4 or more people in for very long), but running the SWG longer not only has it wear out faster, but has the pH rise faster from the increased aeration of the water and possible outgassing of undissolved chlorine gas. So for these reasons and the extra harshness of the higher active chlorine level it makes more sense to use CYA in the water (the table in this post shows this effect).

 

[Cactus345]

2. Buffers the harshness of the chlorine in the water. This is a big factor and suggest you consider it. This is why we recommend CYA for indoor pools even though they do not need protection from the sun. This chart show the "harshness" of the water as a function of FC and CYA level. Your suggested FC level of 2ppm with 0ppm CYA would have an active chlorine level of 0.967. But setting the CYA at 70ppm and maintaining the FC at 5ppm would have an active chlorine level of 0.029 which is 33 times less damaging to skin, hair and suits than what you are doing now.

Thanks for that info, I will add Cya as I didn't realise that the feel of the Cl came into it as you and chem geek have said!

- - - Updated - - -

You will quickly realize reading the forum that test strips are worthless. To truly take control, you need one of the recommended test kits with the FAS-DPD chlorine test.

Also read the article in Pool School about the water balance for SWG pools. We recommend the CYA be in the 70-80ppm range and the corresponding FC shown in the chart in Pool School.

Ok I'll grab a kit from somewhere, thanks, in the meantime I'll up the Cya to 80 by calculating how much to add.

- - - Updated - - -

Great info in post 11, thanks chem geek.

 

[jblizzle]

Unfortunately the critical part of a good test kit is the FAS-DPD chlorine test and that seems to be VERY hard to find in Australia. Most people end up importing it themselves.

 

[Cactus345]

Unfortunately the critical part of a good test kit is the FAS-DPD chlorine test and that seems to be VERY hard to find in Australia. Most people end up importing it themselves.

I haven't looked but no doubt you are right. What kit would you recommend, the TF-100/TF-50 or maybe the Taylor K-2006?

 

[jblizzle]

In the states, the TF-100 is the best value because it comes with more of the reagents that you need. Not sure about getting them sent to you though. I would check what you have locally and then order extra of whatever reagents you can not readily get ... like for the FAS-DPD chlorine test.

 

[yabbyfarm]

I haven't looked but no doubt you are right. What kit would you recommend, the TF-100/TF-50 or maybe the Taylor K-2006?

This the where I get my stuff ordered from.

http://www.poolvacparts.com/taylor-fas-dpd-test-kit-chlorine-service-size.html
takes between 1-2 weeks to get to my door.

 

[Cactus345]

Thanks yabs, that looks good. Anywhere that sells the TF-100 to Oz do you know?

 

[yabbyfarm]

Thanks yabs, that looks good. Anywhere that sells the TF-100 to Oz do you know?

I couldn't find anyone unfortunately.

I forgot to mention. If you order the Taylor 2006 I would recommend ordering a couple of extra reagents at the same time. Specifically I would order
R-0871-C Taylor FAS-DPD Titrating Reagent (Chlorine) 60ml #R-0871-C and
R-0013-C Taylor Cyanuric Acid Reagent 60ml #R-0013-C as they seem to run out quite quickly if you are running a high FC level.

 

[jblizzle]

The TF-100 is only sold by tftestkit.net in the US (and a reseller on the west coast of the US).

To get one, you would likely have to find a person or company to re-ship it to you from out of the US.

I would add that you should order more of the R-0870 FAS-DPD powder as well as the other 2 mentioned above.

 

[Cactus345]

- - - Updated - - -

The TF-100 is only sold by tftestkit.net in the US (and a reseller on the west coast of the US).

To get one, you would likely have to find a person or company to re-ship it to you from out of the US.

I would add that you should order more of the R-0870 FAS-DPD powder as well as the other 2 mentioned above.

That seems very strange, I buy a lot of stuff from the US surely they would want the extra business, they don't have to do anything out of the ordinary to post it here, it's the same procedure. Thanks I'll see what I can do.

- - - Updated - - -

I couldn't find anyone unfortunately.

I forgot to mention. If you order the Taylor 2006 I would recommend ordering a couple of extra reagents at the same time. Specifically I would order
R-0871-C Taylor FAS-DPD Titrating Reagent (Chlorine) 60ml #R-0871-C and
R-0013-C Taylor Cyanuric Acid Reagent 60ml #R-0013-C as they seem to run out quite quickly if you are running a high FC level.

Ok thanks.