CYA loss in salt water pools

[piostrus85]

The direct current in the cell jumps from one plate to another, over time carrying part of the surface with it. That is why the best units reverse the polarity often. The coating is made of metals more resistant to that shedding than the titanium plates are. Same reason a platinum spark plug isn't entire coated with platinum, just the tips where the spark is produced.

And the lack of temperature difference and FC raise is demonstrable. You have a skimmer, you have a return. Take samples, test them, there's your answers.

You have water leaving your heater at well over 100 degrees and you think tiny little plates with a hundred watts of power running through them are heating the water in any measurable way?

The answer here is pretty obvious, but if you happen to have one of these double blind controlled studies you speak of up your sleeve we're always looking for new data to add to the collective.

Oh where do I start?
Direct current does not jump!
It does not carry plates particles with it!
All units reverse polarity but to prevent scale buid up!
Plate coating(Ruthenium) is made of metals highly resistant to aggressive chemical corrosion not"shedding"!
Hypochlorous acid is a very strong oxidizer-it will corrode most metals and make them dissolve.
You need to pay attention to what is said-I never said that plates are heating the water.I said that plates are HOT!
I guess you are one of those people who belives that Sun circles the Earth "because it is so obvious,I can see it"

 

[proavia]

There is zero reason for what is bordering on personal attacks in this thread.
You are free to believe what ever you want to believe and maintain your pool however you see fit.

For a normal residential pool, there is no reason to be able to determine a CYA level as low as the Taylor K-1720 claims to be able to measure. And given the cost of the K-1720, most wouldn't even consider it.

We aren't making rocket fuel here. It's just pool water. And it is constantly exposed to the environment, so is ever changing. What you observe in your pool may not be what I observe in mine. Every pool is different.

CYA degradation in closed pools can happen due to what is believed to be a bacteria that can form in colder water in an unmaintained pool.

In my pool - with or without a SWG - I see higher CYA degradation in the summer months when my pool temp hovers around 90 and the air temps are a low of 90 and high of 110+. In looking thru my records, I see no different in CYA degradation between when I used liquid chlorine and a SWG. Every chlorine pool is a salt water pool and every salt pool is a chlorine pool. When I installed my SWG, my salt content was alread almost 3000 ppm, just from using liquid chlorine and muriatic acid (no additional salt added to get to that level). I tend to run my FC a bit on the hot side and don't notice any greater CYA loss whether the FC is in the target range (FC/CYA Levels) or above the target range. I just test and adjust as needed.

 

[piostrus85]

There is a difference between one's opinion and facts.Unscientific observations do not count as facts and someone's posts with obvious misrepresentations of physics and chemistry should be corrected.

 

[Newdude]

Back on track, was the pool 100 degrees for the regular season when it was uncovered and you noticed the loss ?

 

[piostrus85]

Back on track, was the pool 100 degrees for the regular season when it was uncovered and you noticed the loss ?

Yes.

 

[piostrus85]

CYA history is fascinating.Many "experts" and pool servicers were saying"once you have CYA in your pool it will stay there forever unless you drain the water"Now I see people claiming monthly losses of 20ppm.It seems to me that high enough concentration of oxidizer(chlorine) will destroy it same way as it destroys organic matter.To make things worse measuring CYA concentration is iffy-very inacurate and subjective.20ppm could easily be the margin of error.BTW,same goes for any other pool tests-Cl,pH.On the color scale one can be off by 2 windows.And most people don't want to use ORP meters as a measurement of oxidazing ability of chlorine.

 

[dereksanders]

What was/is the purpose of this thread?

 

[jark87]

What was/is the purpose of this thread?

I came here based on the title. I also experience CYA loss and have wondered why since it is often said here that the only way to reduce CYA is to drain water. We go weeks without rain and I never overfill, so I’ve been left scratching my head. I have a chiller and maintain water temp in the 80s.

I haven’t learned anything yet, but I’ll keep watching!

 

[midlifecrisis]

I came here based on the title. I also experience CYA loss and have wondered why since it is often said here that the only way to reduce CYA is to drain water. We go weeks without rain and I never overfill, so I’ve been left scratching my head. I have a chiller and maintain water temp in the 80s.

I haven’t learned anything yet, but I’ll keep watching!

I too have unexplained CYA loss, greater than what I would expect based on the factors identified here. I have a chiller too and I keep it set at 84f. A couple of weeks ago, I noticed I kept having to raise the output on my SWCG to maintain FC levels. I checked my CYA and I had lost 30ppm since the last time I had checked it. Weird, but this is only my second summer.

I can't explain it, and maybe the experts here can't either, but it feels like the point of this post is to argue without offering solutions, not searching for answers. I'm okay challenging things, but there is a way not to do it.

There might be environmental factors that "we" haven't identified, but this site has proved itself to be about as transparent and ethical as you can get. It might not answer everything, but the principles Dang sure work. That's saying something to me.

Speaking of which, it is time for another donation.

 

[JoyfulNoise]

The plates themselves will barely experience any temperature rise due to the enormous cooling power of the water flowing through the cell. Remember that most SWG flow switches close at 15GPM but most pools tend to run at a flow rate of 30-40GPM or higher. Mosts cells have a volume of about 1 quart (0.25 gallons) and so there is a very large thermal mass of water (typically 70-90F) flowing over the plates. The electronics of the cell, the wiring, and the connectors can all get hot because they tend to have poor contacts which creates contact resistance and power loss (I^2-R heating) but the plates themselves won't be much warmer than the water flowing over them.

As for the cell having "high amounts of chlorine" in it .... do the math. If you assume a cell produces a typical amount of chlorine gas, say 2lbs/day, and you assume the flow rate is somewhere around 30 gallons per minute, then you will typically only have an FC rise inside the cell of around 20-40ppb (parts per BILLION). That additional amount of chlorine pales in comparison to the amount already in the water.

As for the cell itself degrading CYA .... well, you have to understand a little bit about electrochemistry. The chemical reactions that happen at the cell plates happen in a thin film liquid space known as the electrolytic double-layer. It's very detailed physical chemistry but basically any reactant or product at the plate surface has to arrive and leave there by chemical diffusion. The concentrations inside the double-layer are all controlled by reaction rates and chemical diffusivity. The diffusion of cyanuric acid into and out of the double layer is going to be very different than the creation of chlorine, it's subsequent hydrolysis into hypochlorous acid and then its diffusion out of the double layer. Most organic molecules are very slow to diffuse into and out of the double-layer. Most inorganic molecules and ions are fast. So my inclination is to postulate that there is very little degradation that happens at the plate surface.

So where does CYA breakdown? Much more likely in the bulk of the pool water. Chlorine is present but the reaction between chlorine and CYA is very slow. What isn't slow is the reaction of free radicals and organic molecules as those oxidation reactions are very fast. When chlorine breaks down either on its own (autolysis) or from interactions with UV light (photolysis), free radicals (hydroxyl radicals, chlorine radicals, oxygen radicals, etc) are formed. Their reactions with organics like CYA are fast and temperature dependent. This is why pools that are open in hot climates with lots of sun see significant losses in CYA every month (my pool loses about 10ppm per month on average) and pools in more northern climates with fewer high UV Index days see so little. Hot tubs tend to see higher levels of CYA loss because most are maintained at much higher temperatures (>98F) all the time.

 

[piostrus85]

The plates themselves will barely experience any temperature rise due to the enormous cooling power of the water flowing through the cell. Remember that most SWG flow switches close at 15GPM but most pools tend to run at a flow rate of 30-40GPM or higher. Mosts cells have a volume of about 1 quart (0.25 gallons) and so there is a very large thermal mass of water (typically 70-90F) flowing over the plates. The electronics of the cell, the wiring, and the connectors can all get hot because they tend to have poor contacts which creates contact resistance and power loss (I^2-R heating) but the plates themselves won't be much warmer than the water flowing over them.

As for the cell having "high amounts of chlorine" in it .... do the math. If you assume a cell produces a typical amount of chlorine gas, say 2lbs/day, and you assume the flow rate is somewhere around 30 gallons per minute, then you will typically only have an FC rise inside the cell of around 20-40ppb (parts per BILLION). That additional amount of chlorine pales in comparison to the amount already in the water.

As for the cell itself degrading CYA .... well, you have to understand a little bit about electrochemistry. The chemical reactions that happen at the cell plates happen in a thin film liquid space known as the electrolytic double-layer. It's very detailed physical chemistry but basically any reactant or product at the plate surface has to arrive and leave there by chemical diffusion. The concentrations inside the double-layer are all controlled by reaction rates and chemical diffusivity. The diffusion of cyanuric acid into and out of the double layer is going to be very different than the creation of chlorine, it's subsequent hydrolysis into hypochlorous acid and then its diffusion out of the double layer. Most organic molecules are very slow to diffuse into and out of the double-layer. Most inorganic molecules and ions are fast. So my inclination is to postulate that there is very little degradation that happens at the plate surface.

So where does CYA breakdown? Much more likely in the bulk of the pool water. Chlorine is present but the reaction between chlorine and CYA is very slow. What isn't slow is the reaction of free radicals and organic molecules as those oxidation reactions are very fast. When chlorine breaks down either on its own (autolysis) or from interactions with UV light (photolysis), free radicals (hydroxyl radicals, chlorine radicals, oxygen radicals, etc) are formed. Their reactions with organics like CYA are fast and temperature dependent. This is why pools that are open in hot climates with lots of sun see significant losses in CYA every month (my pool loses about 10ppm per month on average) and pools in more northern climates with fewer high UV Index days see so little. Hot tubs tend to see higher levels of CYA loss because most are maintained at much higher temperatures (>98F) all the time.

I did the math and it is 5.5ppm rise-quite high.

 

[AUSpool]

With an Asrtal Viron V25 I should be producing 25g/h of Cl2 with it on 100% output. Enough to raise my FC by 1.3ppm. : Edit. 1.3ppm over an hour or 0.02ppm/minute. So the FC increase is really quite tiny. Then consider that even without factoring in the CyA, HOCl and OCl- are in equilibrium so the active potion of FC is really really tiny. End edit :

Using a Taylor FAS/DPD FC test I could not detect any difference in FC levels between the return water and the bulk water which agrees with the theoretical assumption above.

I can not detect any difference in temperature between the return and bulk water. My solar heating is a stand alone system on its own pump. It provides less then 1 degree in temperature change, its less then I degree Celsius but still enough to feel that the return is warmer then the bulk water and enough to slowly heat the pool. I cant measure or feel any change in temperature from my filter and chlorinator.

 

[piostrus85]

From the manufacturer-pretty sure they have better ways of testing than any poolowners.....
"Think of the RJ-Series as a chlorine generator; set it to create a steady supply of chlorine for the pool, instead of buying and adding chlorine by hand. How it works: Using electrolysis, it creates chlorine from the salt molecules (NaCL) in your water in order to sanitize your pool. A small electric charge is applied across a set of titanium plates inside the Electrolytic Cell. This produces Sodium Hypochlorite (NaOCl). In water, Sodium Hypochlorite dissociates into sodium (NA+) and hypochlorite (OCl-) ions. It is the hypochlorite ions that form with the hydrogen (H+) ions (from the water) to form hypochlorous acid (HOCl), which is the active agent that destroys bacteria and algae, and oxidizes organic matter. This form of chlorine works quickly in the pipe, leaving only a mild residual in the pool. In addition, the Electrolytic Cell continuously “shocks” the incoming water- burning off any oils, organic matter, or other particles that need to be oxidized. Best of all, the process continuously recycles the salt: after cleaning the pool, the original molecules reform and the whole process begins again. The salt doesn't get used up!"

 

[piostrus85]

The plates themselves will barely experience any temperature rise due to the enormous cooling power of the water flowing through the cell. Remember that most SWG flow switches close at 15GPM but most pools tend to run at a flow rate of 30-40GPM or higher. Mosts cells have a volume of about 1 quart (0.25 gallons) and so there is a very large thermal mass of water (typically 70-90F) flowing over the plates. The electronics of the cell, the wiring, and the connectors can all get hot because they tend to have poor contacts which creates contact resistance and power loss (I^2-R heating) but the plates themselves won't be much warmer than the water flowing over them.

As for the cell having "high amounts of chlorine" in it .... do the math. If you assume a cell produces a typical amount of chlorine gas, say 2lbs/day, and you assume the flow rate is somewhere around 30 gallons per minute, then you will typically only have an FC rise inside the cell of around 20-40ppb (parts per BILLION). That additional amount of chlorine pales in comparison to the amount already in the water.

As for the cell itself degrading CYA .... well, you have to understand a little bit about electrochemistry. The chemical reactions that happen at the cell plates happen in a thin film liquid space known as the electrolytic double-layer. It's very detailed physical chemistry but basically any reactant or product at the plate surface has to arrive and leave there by chemical diffusion. The concentrations inside the double-layer are all controlled by reaction rates and chemical diffusivity. The diffusion of cyanuric acid into and out of the double layer is going to be very different than the creation of chlorine, it's subsequent hydrolysis into hypochlorous acid and then its diffusion out of the double layer. Most organic molecules are very slow to diffuse into and out of the double-layer. Most inorganic molecules and ions are fast. So my inclination is to postulate that there is very little degradation that happens at the plate surface.

So where does CYA breakdown? Much more likely in the bulk of the pool water. Chlorine is present but the reaction between chlorine and CYA is very slow. What isn't slow is the reaction of free radicals and organic molecules as those oxidation reactions are very fast. When chlorine breaks down either on its own (autolysis) or from interactions with UV light (photolysis), free radicals (hydroxyl radicals, chlorine radicals, oxygen radicals, etc) are formed. Their reactions with organics like CYA are fast and temperature dependent. This is why pools that are open in hot climates with lots of sun see significant losses in CYA every month (my pool loses about 10ppm per month on average) and pools in more northern climates with fewer high UV Index days see so little. Hot tubs tend to see higher levels of CYA loss because most are maintained at much higher temperatures (>98F) all the time.

"The plates themselves will barely experience any temperature rise due to the enormous cooling power of the water flowing through the cell. Remember that most SWG flow switches close at 15GPM but most pools tend to run at a flow rate of 30-40GPM or higher. Mosts cells have a volume of about 1 quart (0.25 gallons) and so there is a very large thermal mass of water (typically 70-90F) flowing over the plates."
Do you think the heating elements in electric heater also stay cool due to 80 gal of cold water surrounding them?

 

[JoyfulNoise]

I did the math and it is 5.5ppm rise-quite high.

And what do you think the transit time is for a volume of water across the cell plate? Assuming the water enters with 5ppm FC, how much of a rise in FC do you calculate?

(Answer- it’s a really small number)

But let’s play a game and assume that the instant the water enters the cell, the FC rises by 5ppm. So what do you have then, 10ppm FC … that’s not even close to shock level by TFP standards.

Do you think the heating elements in electric heater also stay cool due to 80 gal of cold water surrounding them?

Apples to orange comparison. The heating element inside a heater is designed to dissipate most of the electrical energy as heat from I^2R heating of a metallic element. Also, a heater is closed system most of the time. The volume of water inside the heater is stagnant. When the water does move in a heater (assuming an electric heater from your example), residential flow rates in pipes is less than 5GPM. The heater is designed to ramp up its output to try to maintain a constant water temperature.

By comparison, an SWG is not a heater, it’s an electrolytic cell. You don’t want any of the energy, in a perfect world, to be dissipated as heat but rather used to drive the electrolytic formation of chlorine gas. In fact, if your electrical energy is doing more heating than electrochemistry, then your design is bad. The amount of resistance heating is going to be inversely proportional to the conductivity of the water inside the cell and the salt water is fairly conductive. So the amount of resistance heating is low. As well, the flow rates are much higher and the water volumes are vastly different so there is a huge reservoir of cold water (cold being a relative term) to keep the cell plates from heating much at all.

 

[JamesW]

Current traveling through a metal will create heat, but you do not have enough current traveling through the titanium plates to create a lot of heat.

DC current mostly does not travel through the water.

To heat water, you need AC that can travel through the water.

DC energy mostly gets converted into chemical energy in the form of hydrogen gas and chlorine gas.

The cell essentially operates like a battery charger charging batteries in series with the chemical energy being stored in the hydrogen and chlorine gas.

 

[piostrus85]

Current traveling through a metal will create heat, but you do not have enough current traveling through the titanium plates to create a lot of heat.

DC current mostly does not travel through the water.

To heat water, you need AC that can travel through the water.

DC energy mostly gets converted into chemical energy in the form of hydrogen gas and chlorine gas.

The cell essentially operates like a battery charger charging batteries in series with the chemical energy being stored in the hydrogen and chlorine gas.

"DC current mostly does not travel through the water.

To heat water, you need AC that can travel through the water"
-you know something that physicists don't.

 

[JamesW]

T-15 has 13 Titanium Plates, 150 mm x 63mm x 0.5 mm thick. Produces 1.47 lbs/day.

63mm x 0.5 mm thick = 31.5 mm^2 cross sectional area, which is equal to about a #2 AWG wire.

3 amps going through the equivalent of #2 AWG wire is not going to produce much heat.

You might get about 0.0036 watts of heat from current going through the titanium plate.

A typical T-15 uses about 25 volts and about 7 amps, which is about 175 watts and most of the power/energy is stored in the hydrogen and oxygen and very little gets converted into heat.

Even if the power was all converted into heat, that is about 597.1 btu/hr or 14,330.4 btu/day.

At 30 gpm, that is 43,200 gallons or 360,288 lbs of water.

14,330.4 btu added to 360,288 lb of water is 0.04 degrees.

So, the max temp rise of the water going through the cell is 0.04 degrees if all power is converted into heat.

If 10% is converted into heat, then that is 0.004 degrees for water temp rise.

The Hayward T-Cell uses 13 plates (blades).

The 2 white wires go to the center plate and one black wire goes to each outer plate.

This makes the box and cell work like a battery charger where the water between the plates is the batteries.

Assuming 24 volts DC and 6 amps, it’s like there are 2 sets of (6) 4volt batteries in series being charged with the sets in parallel.

The total amps are 6 amps x 6 cells or 3 amps x 12 cells (36 amps either way).

Amps are the measure of the flow of electrons.

The amperage is directly proportional to the chlorine production and directly proportional to the salinity.

On one side of a plate, a chloride ion loses an electron to become a chlorine radical and then combines with another chlorine radical to create chlorine gas.

So, one electron, one chlorine radical produced.



Anode 4Cl^- -> 2Cl₂.

Cathode 4H₂O -> 2H₂ + 4OH^-.

2Cl₂ +2H₂O -> 3H⁺ + HOCl + OCl^-.

HOCl + OCl^- + uv light -> O₂ + H⁺ + 2Cl^-.

Following the process, we can see that there are 4H⁺ and 4OH^- created, which nets out to pH neutral.

The chlorine gas generated is very acidic and creates 3 hydrogen ions for every 4 hydroxide ions created.

As the hypochlorous acid is broken down by UV, 1 more hydrogen ion is created for a net neutral result.

 

[piostrus85]

And what do you think the transit time is for a volume of water across the cell plate? Assuming the water enters with 5ppm FC, how much of a rise in FC do you calculate?

(Answer- it’s a really small number)

But let’s play a game and assume that the instant the water enters the cell, the FC rises by 5ppm. So what do you have then, 10ppm FC … that’s not even close to shock level by TFP standards.



Apples to orange comparison. The heating element inside a heater is designed to dissipate most of the electrical energy as heat from I^2R heating of a metallic element. Also, a heater is closed system most of the time. The volume of water inside the heater is stagnant. When the water does move in a heater (assuming an electric heater from your example), residential flow rates in pipes is less than 5GPM. The heater is designed to ramp up its output to try to maintain a constant water temperature.

By comparison, an SWG is not a heater, it’s an electrolytic cell. You don’t want any of the energy, in a perfect world, to be dissipated as heat but rather used to drive the electrolytic formation of chlorine gas. In fact, if your electrical energy is doing more heating than electrochemistry, then your design is bad. The amount of resistance heating is going to be inversely proportional to the conductivity of the water inside the cell and the salt water is fairly conductive. So the amount of resistance heating is low. As well, the flow rates are much higher and the water volumes are vastly different so there is a huge reservoir of cold water (cold being a relative term) to keep the cell plates from heating much at all.

"10ppm FC … that’s not even close to shock level by TFP standards"
I was not aware that TFP was setting standards for pools chlorination........

"form hypochlorous acid (HOCl), which is the active agent that destroys bacteria and algae, and oxidizes organic matter. This form of chlorine works quickly in the pipe, leaving only a mild residual in the pool"-this comes from the SWG manufacturer.Should I trust them or the opinions of "experts" in this forum?

 

[piostrus85]

T-15 has 13 Titanium Plates, 150 mm x 63mm x 0.5 mm thick. Produces 1.47 lbs/day.

63mm x 0.5 mm thick = 31.5 mm^2 cross sectional area, which is equal to about a #2 AWG wire.

3 amps going through the equivalent of #2 AWG wire is not going to produce much heat.

You might get about 0.0036 watts of heat from current going through the titanium plate.

A typical T-15 uses about 25 volts and about 7 amps, which is about 175 watts and most of the power/energy is stored in the hydrogen and oxygen and very little gets converted into heat.

Even if the power was all converted into heat, that is about 597.1 btu/hr or 14,330.4 btu/day.

At 30 gpm, that is 43,200 gallons or 360,288 lbs of water.

14,330.4 btu added to 360,288 lb of water is 0.04 degrees.

So, the max temp rise of the water going through the cell is 0.04 degrees if all power is converted into heat.

If 10% is converted into heat, then that is 0.004 degrees for water temp rise.

The Hayward T-Cell uses 13 plates (blades).

The 2 white wires go to the center plate and one black wire goes to each outer plate.

This makes the box and cell work like a battery charger where the water between the plates is the batteries.

Assuming 24 volts DC and 6 amps, it’s like there are 2 sets of (6) 4volt batteries in series being charged with the sets in parallel.

The total amps are 6 amps x 6 cells or 3 amps x 12 cells (36 amps either way).

Amps are the measure of the flow of electrons.

The amperage is directly proportional to the chlorine production and directly proportional to the salinity.

On one side of a plate, a chloride ion loses an electron to become a chlorine radical and then combines with another chlorine radical to create chlorine gas.

So, one electron, one chlorine radical produced.

View attachment 611430

Anode 4Cl^- -> 2Cl₂.

Cathode 4H₂O -> 2H₂ + 4OH^-.

2Cl₂ +2H₂O -> 3H⁺ + HOCl + OCl^-.

HOCl + OCl^- + uv light -> O₂ + H⁺ + 2Cl^-.

Following the process, we can see that there are 4H⁺ and 4OH^- created, which nets out to pH neutral.

The chlorine gas generated is very acidic and creates 3 hydrogen ions for every 4 hydroxide ions created.

As the hypochlorous acid is broken down by UV, 1 more hydrogen ion is created for a net neutral result.

You like the battery analogy-great.Have you ever touched a battery being charged?
Why everyone is talking about water temperature rise?I stated that plates get hot.Water temperature rise is irrelevant.
You got the reaction occuring on cathode completly wrong.