Granular and Liquid chlorine

[Fishy1234]

Some of the local pool owners are advising using granular chlorine during the week, and liquid chlorine after a pool party or once a week. They claim that the granular last longer in the summer than liquid which burns off fast.
Also they switch to liquid in winter months because chlorine is not needed as much.
Does this sound like good advice? I am currently using a gallon every other day.

 

[magiteck]

Some of the local pool owners are advising using granular chlorine during the week, and liquid chlorine after a pool party or once a week. They claim that the granular last longer in the summer than liquid which burns off fast.
Also they switch to liquid in winter months because chlorine is not needed as much.
Does this sound like good advice? I am currently using a gallon every other day.

Hi fishy,

Their advice is a bit misguided. The stabilized chlorine they are recommending is adding CYA to the water— which it’s true, that will help to reduce chlorine loss.

However, that CYA doesn’t get consumed with the chlorine, and builds up, making your chlorine continuously less effective.

It’s true that you do want some CYA (stabilizer) in your water. But once you have the right amount of it, you don’t want to add more. At that point, your liquid chlorine will be protected by the CYA already in your water. As you add more liquid chlorine, it will continue to bind with and be protected by your existing CYA.

Have a read through ABCs of Pool Water Chemistry for some better understanding of the chemistry. Ultimately you want your chlorine and CYA to maintain a ratio, as shown in the FC/CYA Levels. If you’re adding more CYA every time you add chlorine, you can’t maintain those ratios and eventually your water will be compromised — typically with algae as the first sign.

Trust your Taylor test kit, follow the FC/CYA chart, stick to the liquid chlorine, and you’ll be in good shape!

 

[Fishy1234]

Hi fishy,

Their advice is a bit misguided. The stabilized chlorine they are recommending is adding CYA to the water— which it’s true, that will help to reduce chlorine loss.

However, that CYA doesn’t get consumed with the chlorine, and builds up, making your chlorine continuously less effective.

It’s true that you do want some CYA (stabilizer) in your water. But once you have the right amount of it, you don’t want to add more. At that point, your liquid chlorine will be protected by the CYA already in your water. As you add more liquid chlorine, it will continue to bind with and be protected by your existing CYA.

Have a read through ABCs of Pool Water Chemistry for some better understanding of the chemistry. Ultimately you want your chlorine and CYA to maintain a ratio, as shown in the FC/CYA Levels. If you’re adding more CYA every time you add chlorine, you can’t maintain those ratios and eventually your water will be compromised — typically with algae as the first sign.

Trust your Taylor test kit, follow the FC/CYA chart, stick to the liquid chlorine, and you’ll be in good shape!

One of the problems I am seeing with using liquid chlorine is that the ph is 13 so ph in pool rises and it causes salt level to rise. Eventually the pool water needs to be partially drained due to high salt level.

 

[mguzzy]

One of the problems I am seeing with using liquid chlorine is that the ph is 13 so ph in pool rises and it causes salt level to rise. Eventually the pool water needs to be partially drained due to high salt level.

The chlorine is diluted when you put it in your water. There is very little pH change. And yes, it decomposes into salt but the amount is very little. It would take years (like decades) of liquid chlorine use to get your pool's salinity up to 1500 ppm. SWG chlorinators operate at salinities in the 2700-3700 ppm range. (One gal adds 4.1ppm of salt in a 40K pool) And winter rains would dilute it as well. So you really don't have anything to worry about. Please read through the ABCs of Pool Water Chemistry, there is a lot of useful information about how pool chems work. Also peruse the effects of adding in the PoolMath app.

 

[magiteck]

One of the problems I am seeing with using liquid chlorine is that the ph is 13 so ph in pool rises and it causes salt level to rise. Eventually the pool water needs to be partially drained due to high salt level.

I’m not a chemist by any means, but from my readings here, the small volume of high pH bleach does cause a small pH increase. However the process of the chlorine breaking down causes an acidic reaction which essentially makes the effect of the liquid chlorine pH neutral.

pH rise then is typically because of aeration of the water (splashing, etc). Stabilized chlorine is acidic and so pools using that exclusively often have the opposite problem — pH too low.

Acid is needed occasionally to counter the pH rise from liquid chlorine. Once you find the sweet spot with your alkalinity that becomes less frequent. I use LC exclusively and only added acid once last Summer. Otherwise my pH stated comfortably in the 7’s.

High salt levels, at least at the level that chlorine products are adding, aren’t really a problem.

 

[mguzzy]

I’m not a chemist by any means, but from my readings here, the small volume of high pH bleach does cause a small pH increase. However the process of the chlorine breaking down causes an acidic reaction which essentially makes the effect of the liquid chlorine pH neutral.

That is correct!

 

[Fishy1234]

My 3 year old non salt pool was at 4400 ppm salt last November and was consuming liquid chlorine and muriatic acid daily. I drained 2 feet of the 5ft deep water in November and salt water level went down to 2200ppm. It is now at 2600ppm.

 

[mguzzy]

Lets do some Math. If you are going through 1 gallon every two days over the course of three years that is (365x3)/2=547.5 gallons of chlorine. That by the way is about what I would expect over the course of the year of FC usage per day. 1 gallon of 10% chlorine will raise your FC 4.5 ppm. At the height of the summer most pools loose 4-5 ppm FC/per day and less than 1 ppm in the winter. That is average. I don't think you are dumping in a half gallon per day in the winter but for the sake of argument lets say you are. For each gallon of chlorine pool math shows a 7.5 ppm addition of salt in a 22K pool. So that is 547.5 x 7.5=4106 ppm. So that puts you in the ball park for 4400 ppm salinity. But you must have a cover on your pool or it never rains there. I know its kind of arid in Apple Valley. Nor must you have any splash out. And it doesn't take into account other chems that degrade into salt, nor the properties of your fill water. My pool is about the same size and I usually lose about 250 to 500 ppm a year from mostly rain dilution. Still 4400 ppm is nothing to worry about. SWG users have their salinity at that level all the time. Many people add salt to their pools even when they don't have an SWG just cause they like the feel of it. I just saw a post by a user that wanted to raise the salinity in their pool to 10,000ppm for use as a therapy pool.

 

[Fishy1234]

Lets do some Math. If you are going through 1 gallon every two days over the course of three years that is (365x3)/2=547.5 gallons of chlorine. That by the way is about what I would expect over the course of the year of FC usage per day. 1 gallon of 10% chlorine will raise your FC 4.5 ppm. At the height of the summer most pools loose 4-5 ppm FC/per day and less than 1 ppm in the winter. That is average. I don't think you are dumping in a half gallon per day in the winter but for the sake of argument lets say you are. For each gallon of chlorine pool math shows a 7.5 ppm addition of salt in a 22K pool. So that is 547.5 x 7.5=4106 ppm. So that puts you in the ball park for 4400 ppm salinity. But you must have a cover on your pool or it never rains there. I know its kind of arid in Apple Valley. Nor must you have any splash out. And it doesn't take into account other chems that degrade into salt, nor the properties of your fill water. My pool is about the same size and I usually lose about 250 to 500 ppm a year from mostly rain dilution. Still 4400 ppm is nothing to worry about. SWG users have their salinity at that level all the time. Many people add salt to their pools even when they don't have an SWG just cause they like the feel of it. I just saw a post by a user that wanted to raise the salinity in their pool to 10,000ppm for use as a therapy pool.

You wrote a lot. I do appreciate hearing that you are telling how 1 gallon of 10 percent chlorine will increase 4.5 ppm in my pool and that is exactly my case.
What I did see happen after draining 2 feet of my 5 foot deep pool was the chlorine level became stable, as well as the Alkalinity. So from November to March I was only using about 1/2 a gallon of chlorine every 2-3 days. I hardly used Muriatic acid. Then the temperature went up and chlorine usage up as well. Alkalinity is still stable 70-80 ppm.

 

[mguzzy]

Draining half your water also lowered your CYA.. if it was too high that would account for more stable FC. I would need to see test numbers from before and after your drain and refill to get a better idea of what happened. Yep that's what happen when summer hits.. the higher sun in the sky will degrade more Chl.. some people bump their CYA to compensate.

 

[Fishy1234]

Draining half your water also lowered your CYA.. if it was too high that would account for more stable FC. I would need to see test numbers from before and after your drain and refill to get a better idea of what happened. Yep that's what happen when summer hits.. the higher sun in the sky will degrade more Chl.. some people bump their CYA to compensate.

Okay so prior to drain if I recall CYA was 80.
Just to try it my neighbor gave me 2 bags of granular chlorine. It has Chlor-brite on the 1 pound bags. My FC was down to 4.0 before I added 1 1/2 bags last night. I want to see if the chlorine will last longer in this heat as he claims.
Today's measurement FC 8.0. CH400, Alk70, PH7.7.

 

[magiteck]

Okay so prior to drain if I recall CYA was 80.
Just to try it my neighbor gave me 2 bags of granular chlorine. It has Chlor-brite on the 1 pound bags. My FC was down to 4.0 before I added 1 1/2 bags last night. I want to see if the chlorine will last longer in this heat as he claims.
Today's measurement FC 8.0. CH400, Alk70, PH7.7.

The 1.5lbs of dichlor you added should have raised your FC by ~4.6, but will also have raised your CYA by ~4.2.

Because you’ve added more CYA, you’ll likely see it last a small amount longer. However, you’ve now also slightly increased your minimum chlorine level for proper sanitation.

What was your CYA level prior to adding the dichlor?

 

[Rancho Cost-a-Lotta]

Fishy,

Be careful with Chlor-Brite. It's dichlor. 24 oz. will raise your FC level by 4.6 ppm, but will also raise your CYA level by 4.2 ppm. The chlorine won't last any longer than liquid chlorine. You will lose the same amount of FC daily, regardless of the form of chlorine you put in the pool.

Dichlor is acidic and will stain your plaster. If you use it, make sure it's fully dissolved and not allowed to remain on the pool floor.

Edit...looks like @magiteck beat me too it...

 

[Fishy1234]

The 1.5lbs of dichlor you added should have raised your FC by ~4.6, but will also have raised your CYA by ~4.2.

Because you’ve added more CYA, you’ll likely see it last a small amount longer. However, you’ve now also slightly increased your minimum chlorine level for proper sanitation.

What was your CYA level prior to adding the dichlor?

CYA was 4.0 before adding.

 

[Fishy1234]

Fishy,

Be careful with Chlor-Brite. It's dichlor. 24 oz. will raise your FC level by 4.6 ppm, but will also raise your CYA level by 4.2 ppm. The chlorine won't last any longer than liquid chlorine. You will lose the same amount of FC daily, regardless of the form of chlorine you put in the pool.

Dichlor is acidic and will stain your plaster. If you use it, make sure it's fully dissolved and not allowed to remain on the pool floor.

Edit...looks like @magiteck beat me too it...

I noticed how it settled to the bottom, so I brushed the floor.

 

[mguzzy]

Okay so prior to drain if I recall CYA was 80.
Just to try it my neighbor gave me 2 bags of granular chlorine. It has Chlor-brite on the 1 pound bags. My FC was down to 4.0 before I added 1 1/2 bags last night. I want to see if the chlorine will last longer in this heat as he claims.
Today's measurement FC 8.0. CH400, Alk70, PH7.7.

I don't see the reason for the experiment.. the experimenting has already been done.. and the result is the FC/CYA Levels.. follow it and life will be grand.

 

[Newdude]

follow it and life will be grand.

And many many grand$ will stay in your pocket and not the pool store’s cash register.

 

[magiteck]

CYA was 4.0 before adding.

Did you mean 40? 4.0 isn’t a valid result for the CYA test. I think the minimum your K2006 can measure is 30.

 

[Oly]

My 3 year old non salt pool was at 4400 ppm salt last November and was consuming liquid chlorine and muriatic acid daily. I drained 2 feet of the 5ft deep water in November and salt water level went down to 2200ppm. It is now at 2600ppm.

This too was my experience after almost 4 years of using liquid Cl in a fresh fill. I drained a bit of the water and refilled to drop the NaCl to 3500 then installed a SWG system. Game changer.

 

[Fishy1234]

Did you mean 40? 4.0 isn’t a valid result for the CYA test. I think the minimum your K2006 can measure is 30.

Yes 40