Help with Stabilizer - Relative newbie

[cbecke]

Hi.

Since I occasionally teach high school chemistry, I've been recruited by my neighborhood in Virginia to run chemicals for the pool, an in-ground 4 lane, 200,000 gallon pool. We use liquid chlorine and HCl to manage pH. I've got the hang of adding Calcium chloride to maintain proper hardness levels and sodium bicarbonate to maintain proper alkalinity.

The levels for chlorine, pH, hardness and alkalinity have all been maintained in an acceptable range over the past 3 years that I've been doing this.

But I haven't figured out stabilizer yet. I added what seemed to be quite a bit of cyanuric acid (15 pounds?) but didn't see any rise in the levels as I tested.

My questions:

1) How much cya is necessary for a pool this size?

2) If I can get the cya to proper levels, how much will it reduce the chlorine use?

3) How "acidic" is cya, in terms of will it reduce the pH too much if I add it all at once? My concern is if the chlorine level is right and the cya reduces the pH, I can't add chlorine to raise the pH, as it is now stabilized and will remain at too high a level. does that make sense?

So, any suggestions or links to threads where this has already been answered would be quite helpful.

Thanks.

- Chris

 

[tim5055]

Welcome to the TFP pool! :splash:

The first question we always ask, what are you using to test with?

Second, ignore the fact that chlorine is a base and will raise pH. The use of liquid chlorine is actually a pH neutral event. pH goes up when you add it but there is an opposite reaction when it oxidizes contaminates in the pool. The best way to raise pH is aeration.

CYA is an acid, but it has little effect on the pool pH when added.

You will find that our recommendations generally conflict with the pool "industry", but the biggest difference is we tend to use either a salt water chlorine generator or liquid chlorine which you also use. We shy away from solid forms of chlorine because they tend to bring stuff to the pool water solution we doen't want in excess, like CYA and calcium.

We generally recommend new members read these articles to get the basics of our recommendations.

ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

When you get to that point, add the CYA by using what we call the sock method. Get an old sock (no holes in the toes) and put the measured amount of CYA you need to get to your first target. Tie the sock closed and either suspend it in front of a return (hang it from your brush pole works with something weighted on the deck) OR if it still allows flow thru the skimmer, place the sock in the skimmer. Every 15/20 minutes give the sock a squeeze to speed up the process or just leave it alone, your choice. Please DO NOT follow the directions on the container of CYA to just pour it into the skimmer and don't just toss the sock in the pool as the CYA is acidic and can bleach/stain pool finishes.

We also like to see folks add chemicals like CYA in stages. In your case, add enough to target 30 and wait to see the results. If the final goal is higher due to a salt water chlorine generator or a pool in a very sunny location then we might target 50, then target the final 70. Doing it in stages allows you to make sure you don't overshoot your goal. We find that many people are slightly "off" on the volume of their pool, so it's easy to add too much of a chemical. At first, just stick with 30 as your target.

Please edit your signature and add the following information so we can better frame our answers to you.

• List what test kit you use to test your water
  
• The size of your pool in gallons
  
• If your pool is an AG (above ground) or IG (in ground)
  
• If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
  
• The type filter you have (sand, DE, cartridge)
  
• If you know, tell us the make and model of your pump and filter.
  
• List any other equipment you have: SWG, second pump, etc.
  
• Please mention if you fill the pool from a well or are currently on water restrictions

Information in your signature will show up each time you post and it makes advice more accurate as we know what equipment we are dealing with.

 

[ajw22]

This an indoor pool or outdoor pool? Indoor pools have different CYA needs then the outdoor pools we usually talk about here. Indoor pools don't need all the sunlight protection CYA provides.

 

[cbecke]

This is an outdoor pool. We go through lots of chlorine, and it's sometimes a challenge to maintain proper levels. The chlorine pump may be under undue strain due to running so often.

Is there a "pounds of cya per gallon to ppm" conversion table or calculator somewhere?

And is there an alternative to the sock method? My neighbors might not appreciate socks filled with chemicals in the neighborhood pool.

(oh, and I've added a signature )

 

[ajw22]

Is there a "pounds of cya per gallon to ppm" conversion table or calculator somewhere?

PoolMath

 

[cbecke]

Thanks

 

[mknauss]

Welcome to the forum! :handshake:

I am curious - your first post said 200,000 gallon and your signature says 105,000 gallons. Can you confirm which is correct? It will help us help you if you have chemistry questions.

Which Taylor kit are you using? Please put the model number in your signature.

 

[sehrmude]

And is there an alternative to the sock method? My neighbors might not appreciate socks filled with chemicals in the neighborhood pool.

(oh, and I've added a signature )

Liquid stabilizer - but it is more costly. I use it, but I only have a 10,500 gallon pool with 2 adults using it (very little splash out to require replenishment)...the cost offset vs ease of dosing isn't that big for me.

 

[tim5055]

And is there an alternative to the sock method? My neighbors might not appreciate socks filled with chemicals in the neighborhood pool.

(oh, and I've added a signature )

Thanks for the signature, it helps. But as Marty pointed out, the specific kit makes a difference.

Your request for an alternative to the "sock" brings up an interesting point. Trouble Free Pool (TFP) is geared toward individual residential pool owners. I'm not sure of Virginia (or any subdivision of the state) law or regulation regarding your pool. Many states define a neighborhood pool as a "public" pool and have specific requirements on how the pool is to be maintained. One of those regulations that is common is that no chemicals can be added to the pool while bathers are present. They usually exclude chlorine and acid injection systems.

So, please take any advice you get here with a grain of salt and make sure you are following any/all regulations in your area.

So, if you can dispense chemicals while the pool is open you can still put it in a sock and place the sock inside a skimmer (don't block all the flow). I have found that if you give the sock a friendly squeeze every 15/20 minutes it is dissolved into solution within a couple of hours.

Oh, and as a science teacher, I searched around for the details of liquid chlorine being a pH neutral event

I'll do this in words and in symbols. Adding bleach is a basic process; it is the using up of bleach (chlorine) that is an acidic process so the net result is almost neutral. When I said "chlorine usage" I didn't mean your using chlorine (i.e. adding it) -- I meant when chlorine gets used up by "doing its thing" or "breaking down". Sorry for the confusion I caused.

Adding Chlorine
NaOCl + H₂O --> Na⁺ + HOCl + OH^- (+ extra base Na⁺ + OH^-)
HOCl --> H⁺ + OCl^-
Sodium Hypochlorite (liquid chlorine or bleach) combines with water to produce sodium ions (part of regular table salt) plus disinfecting chlorine plus hydroxyl ion. The hydroxyl ion makes this a basic reaction that raises pH, but because the disinfecting chlorine is a weak acid this overall reaction raises the pH by less than a strong base would. Note that there is a small amount of extra base in the form of Sodium Hydroxide (lye or caustic soda) that comes with Sodium Hypochlorite and is there to help preserve it, but this amount is rather small.

Using Up Of Chlorine
Breakdown of Chlorine by Sunlight (UV)
2HOCl --> O₂(g) + 2H⁺ + 2Cl^-
2OCl^- --> O₂(g) + 2Cl^-
Chlorine breaks down in the presence of ultraviolet radiation, such as found in sunlight, and forms oxygen gas and chloride ion (and hydrogen ion, if starting with HOCl hypochlorite). Because a hydrogen ion is produced, this is an acidic process, but since disinfecting chlorine is a weak acid, only some of it breaks down in a way that lowers pH as shown above (i.e. only HOCl produces H⁺; OCl^- does not). During the process of chlorine breakdown by sunlight, there are hydroxyl (OH•), oxygen anion (O^-•) and chlorine (Cl•) radicals that are also produced as short-lived intermediates (technical details in this post). This can help oxidize organics in the pool.

Richard

 

[cbecke]

I thought the Taylor test kits were all the same, but now I see they're not. I believe it's a K2005C kit.

I was remembering 200k gallons, but I found a previous document that reminded me I did my best calculation of 105k gallons. This information wasn't readily available from the neighborhood historian, as we don't have one!

 

[tim5055]

I thought the Taylor test kits were all the same, but now I see they're not. I believe it's a K2005C kit.

The 2005C is a quality kit, it is just missing the single most important test that we base our system of pool care on. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential. The K-2006-C has teh FAS/DPD while the K-2005-C has the DPD chlorine test.

Purchase this one test and your 2005 becomes a 2006.

 

[cbecke]

I will, of course, hold TFP, its forums and its participants free from any liability I may incur in my volunteer role taking care of the neighborhood pool!

That said, it never hurts to learn more.

My thought about acid/base is that if the addition and breakdown of chlorine was a net neutral set of processes, then we shouldn't need an acid feed in the first place. So there must be something else going on there.

I'll use the pool math calculator and try the sock method in a skimmer to start bringing up the stabilizer. We've gone this far without it, so if it takes me a week to bring it up to target, I should be in good shape and will see if our use of chlorine can decrease.

Thanks for the assistance.

 

[tim5055]

My thought about acid/base is that if the addition and breakdown of chlorine was a net neutral set of processes, then we shouldn't need an acid feed in the first place. So there must be something else going on there.

Almost all pools have a naturally rising pH. Yours probably more due to a bunch of splashing kids. Aeration is a great way to raise your pH.

 

[cbecke]

The 2005C is a quality kit, it is just missing the single most important test that we base our system of pool care on. To effectively practice the TFPC methods, the FAS/DPD chlorine test is essential. The K-2006-C has teh FAS/DPD while the K-2005-C has the DPD chlorine test.

I'll have to look at the kit to get the number to see which it is. They look very much the same on the Taylor site.

Do you have a link to the difference between the FAS/DPD and just the DPD tests?

 

[MannyT]

The FAS/DPD kit has a small round container with a powder to indicate chlorine. The DPD kit doesn't uses liquid to show your chlorine.

 

[tim5055]

As Manny indicates, the FAS/DPD is a two part test. You add a powder to turn the water sample pink and then add drops counting them until the solution turns clear

The DPD test is a color match test. Add solution ot a tube and add DPD liquid. Then match the color standards along the side.

 

[cbecke]

We definitely use the DPD color match test.

So is the FAS/DPD test more accurate? Or does it provide additional information?

 

[mknauss]

More accurate and can read FC to higher levels. FAS-DPD can read to 50 ppm FC. Your DPD is good to 10 ppm FC.

To SLAM a pool you must have a FAS-DPD test.

 

[cbecke]

More accurate and can read FC to higher levels. FAS-DPD can read to 50 ppm FC. Your DPD is good to 10 ppm FC.

To SLAM a pool you must have a FAS-DPD test.

We had an "incident" and to shock and read the higher chlorine levels, we diluted 1/2 cup pool water with 1.5 cups distilled water and then multiplied the resulting DPD test result by 4. It seemed a clever way to work around the limited range of the test, given available materials.

 

[mknauss]

That was good to get an approximate value of elevated FC. But certainly not accurate.

The FAS-DPD can easily measure down to 0.2 ppm FC, though we recommend using a 10ml sample of water which gives a 0.5ppm FC resolution.