Difference between revisions of "PH TA Relationship" - Further Reading

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[[Category:Swimming Pool Chemistry]]
 
[[Category:Swimming Pool Chemistry]]
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:Maintaining pH within a certain range is important because it can have an effect on plaster, liners, equipment and most importantly on people.  TA levels have fewer effects on the pool than pH.  Except in a limited number of situations, TA and pH generally move in tandem.  If you increase TA, pH generally increases.  If you lower TA, pH generally decreases.  This article will explore the relationship between TA and pH and pH rise and acid demand.
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'''To reduce the rate of pH rise, you can reduce your Total Alkalinity until your pH rise is manageable.  This article explains the chemistry behind pH rise and reducing Total Alkalinity.'''
  
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'''If you are looking to learn how to manage TA and pH, check here [[Managing pH and Total Alkalinity]]'''
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:'''If you want learn how to manage TA and pH, check here [[Managing pH and Total Alkalinity]]'''
  
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'''If you want to understand the causes of rising pH and how to slow it, check here [[Managing pH and Total Alkalinity#Causes, and reducing pH rise|]]'''
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:'''If you want to understand the causes of rising pH and how to slow it, check here [[Managing pH and Total Alkalinity#Causes, and reducing pH rise|Causes, and reducing PH rise]]'''
  
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=Causes of rising pH=
 
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:The level of aqueous (dissolved) CO2 in pool water determines how fast pH will rise.  For a deep dive, start here  [[#pH TA relationship - The Deep End|pH TA relationship - The Deep End]].  Many pool owners experience constant acid demand and pH rises quickly, requiring constant additions of acid.  There are several causes of high levels of CO2, rising pH and acid demand:
 
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:# Water features and aeration release CO2
 
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:# Lower pH water has higher levels of CO2
 
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:# Higher levels of TA allow higher levels of CO2
 
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:# When pool water has low pH and high TA, it has the most amount of stored CO2
 
  
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:pH levels have a larger influence on CO2 levels (and pH rise) than TA levels.  For explanation, see [[#pH TA relationship - The Deep End|pH TA relationship - The Deep End]]
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==Summary==
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:'''<big>If your pH rise is rapid and difficult to reasonably manage, reduce your TA to the point your pH rises at a rate that you CAN reasonably manage. Worry about pH (keep it in range) and pH rise (what you can manage), worry less about the absolute TA number (except to keep it at least 50).</big>'''
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==Reducing pH rise and acid demand==
 
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:For a deep dive on the causes of rising pH, start here [[#pH TA relationship - The Deep End|pH TA relationship - The Deep End]].
 
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:Water features and aeration cause the release of CO2, which raises pH.  The ways to combat this are to turn off the aeration or limit the time that one runs the water feature. 
 
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:Practically, as pH rises, the rate of rise will slow.  If the pH rise is faster than you care to maintain, [https://www.troublefreepool.com/blog/2019/01/18/lower-total-alkalinity/ reduce your TA] until the rate of rise is reasonable to manage.  There will become a point where the TA is sufficiently low, and your pH will slow to a reasonable level. In many pools, particularly SWCG pools, the TA level may be as low as 50 and the resulting pH may be at 7.8-8.0.  All pools are different, you need to find the right level for your pool.
 
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:A reasonable starting point for most pools is a TA of 80-100.  Most find however, particularly with SWCG pools, that a TA of 60-80 slows their pH rise sufficiently, hence the TFP [https://www.troublefreepool.com/threads/updated-recommended-levels.199663/ recommended levels]. TA can be safely lowered as far as 50 ppm if necessary.  Keeping your TA on the low end will not “rot out your equipment” or “destroy your plaster surfaces”.  The TA range in the Recommended Levels is designed to protect your pool surface as long as the pH, TA, and CH can be kept in recommended ranges.
 
  
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:The scope of this article is to help you understand the TA, pH relationship and to better manage the two.  It will not get you to a permanent, zero acid demand pool.  It will significantly extend the period between acid additions.
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:1) The higher the Aqueous (dissolved) CO2 levels in the pool, the faster pH will rise.
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==If TA in the water contributes to pH rise, can I just get rid of all the TA?==
 
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:TA levels below about 50 ppm lead to insufficient levels of TA to buffer pH to prevent sudden pH crashes.
 
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==Why should one ignore TA if their pH is steady?==
 
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:You now understand the relationship between TA and pH, and that one of the primary objective of TFP is to have a pool that has reasonable rising pH levels and acid demand.  Once you have achieved reasonably steady pH, you have met the objective.  Your pool is in reasonable equilibrium.  Sit back and enjoy!
 
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=pH TA relationship - The Deep End=
 
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==Summary==
 
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:1) The higher the Aqueous (dissolved) CO2 levels the faster pH rise.
 
 
:2) Lower pH water has higher levels of CO2
 
:2) Lower pH water has higher levels of CO2
 
:3) Higher levels of TA allow higher levels of CO2
 
:3) Higher levels of TA allow higher levels of CO2
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:4) Combined, lower the pH and higher TA, will lead to the pool wanting to outgas CO2, resulting faster pH rise.
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:4) When pH is low AND Total Alkalinity is high, the pool has the highest levels of CO2, resulting in the fastest pH rise.
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:5) Reducing your TA until you have a fairly stable pH, reduces the need to constantly add [[Acid]]
 
  
 
==Henry’s Law & Pools==
 
==Henry’s Law & Pools==
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==pH and TA==
 
==pH and TA==
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:Total alkalinity (TA) is the measure of water's ability to neutralize acids. The role of alkalinity (TA to make is simple) is to buffer (slow down) a reduction in pH. When acid is added, carbonate ions can absorb Hydrogen to create bicarbonate ions. And with enough acid, bicarbonate ions absorb another Hydrogen ion and convert into carbonic acid, which is dissolved CO2. The reverse of our equations above.
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:Total alkalinity (TA) is the measure of water's ability to neutralize acids. The role of TA is to buffer (slow down) a reduction in pH. When acid is added, carbonate ions can absorb Hydrogen to create bicarbonate ions. And with enough acid, bicarbonate ions absorb another Hydrogen ion and convert into carbonic acid, which is dissolved CO2. The reverse of our equations above.
  
 
:Net, net, having alkalis (like Carbonate/Bicarbonate) in the pool allow CO2 to be stored in the pool.  More CO2 in the pool, the more the pool wants to outgas CO2.  The more the pool wants to outgas CO2, the faster pH will rise.
 
:Net, net, having alkalis (like Carbonate/Bicarbonate) in the pool allow CO2 to be stored in the pool.  More CO2 in the pool, the more the pool wants to outgas CO2.  The more the pool wants to outgas CO2, the faster pH will rise.
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:*If the number is Red (>20), there is a large pressure on the water to outgas CO2 and you would see a faster rise in pH.
 
:*If the number is Red (>20), there is a large pressure on the water to outgas CO2 and you would see a faster rise in pH.
  
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:Conclusion: To reduce your pool's rate pH rise rate to a level you can reasonably manage, reduce your TA to the point your pH rises at a rate that you can reasonable manage. Worry about pH (keep it in range) and pH rise (what you can manage), worry less about the absolute TA number (except to keep it above 50).
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:'''<big>If your pH rise is rapid and difficult to reasonably manage, reduce your TA to the point your pH rises at a rate that you CAN reasonably manage. Worry about pH (keep it in range) and pH rise (what you can manage), worry less about the absolute TA number (except to keep it at least 50).</big>'''
  
 
[[File:CO2_Out_of_Equilibrium.jpg|Frameles|center|link=https://www.troublefreepool.com/wiki/images/d/d2/CO2_Out_of_Equilibrium.jpg]]
 
[[File:CO2_Out_of_Equilibrium.jpg|Frameles|center|link=https://www.troublefreepool.com/wiki/images/d/d2/CO2_Out_of_Equilibrium.jpg]]

Latest revision as of 00:05, 23 April 2024

To reduce the rate of pH rise, you can reduce your Total Alkalinity until your pH rise is manageable. This article explains the chemistry behind pH rise and reducing Total Alkalinity.

If you want learn how to manage TA and pH, check here Managing pH and Total Alkalinity
If you want to understand the causes of rising pH and how to slow it, check here Causes, and reducing PH rise


Summary

If your pH rise is rapid and difficult to reasonably manage, reduce your TA to the point your pH rises at a rate that you CAN reasonably manage. Worry about pH (keep it in range) and pH rise (what you can manage), worry less about the absolute TA number (except to keep it at least 50).
1) The higher the Aqueous (dissolved) CO2 levels in the pool, the faster pH will rise.
2) Lower pH water has higher levels of CO2
3) Higher levels of TA allow higher levels of CO2
4) When pH is low AND Total Alkalinity is high, the pool has the highest levels of CO2, resulting in the fastest pH rise.

Henry’s Law & Pools

Henry's law is one of the gas laws formulated by William Henry in 1803 and states: "At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid."
In terms most of us can understand, Henry's law basically states that the amount of a gas dissolved in water wants to be directly proportional to the amount of that same gas in the atmosphere. Our atmosphere has a small percentage of CO2, so CO2 leaves the pool (or outgasses) trying to equalize with the atmosphere. This process is not immediate, it happens over a time.

CO2 and Water

CO2 dissolves in water, and some of it reacts with water molecules to produce a slightly acid solution called carbonic acid. The (aq) indicates water solution.
CO2(aq) + H2O ←→ H2CO3(aq)​
Carbonic acid is weak, so some of it dissociates to produce H+ ions, hence it’s a slightly acidic solution, forming the hydrocarbonate ion, and Bicarbonate, and with release of more H+ ions, Carbonate.
H2CO3(aq) ←→ H+(aq) + HCO3-(aq) And HCO3-(aq) ←→ H+(aq) + CO3–2(aq)
All These are all reversable.

pH and CO2

pH is a measure of how basic/acidic water is. pH is measured by the concentration of Hydrogen (H+) and hydroxyl ions in water. So, the more CO2 in water, the more H+ ions in the water, the more acidic and the lower the pH.
Remember Henry’s law... Our atmosphere tends to have less CO2 than our pools, so the CO2 in our pools desires to be in equilibrium with the atmosphere, as a result, CO2 outgasses, reducing the H+ ions, increasing pH.

pH and TA

Total alkalinity (TA) is the measure of water's ability to neutralize acids. The role of TA is to buffer (slow down) a reduction in pH. When acid is added, carbonate ions can absorb Hydrogen to create bicarbonate ions. And with enough acid, bicarbonate ions absorb another Hydrogen ion and convert into carbonic acid, which is dissolved CO2. The reverse of our equations above.
Net, net, having alkalis (like Carbonate/Bicarbonate) in the pool allow CO2 to be stored in the pool. More CO2 in the pool, the more the pool wants to outgas CO2. The more the pool wants to outgas CO2, the faster pH will rise.

So What?

Your pool wants to be in some form of equilibrium, and that is affected by the pH and the TA of the water. If we were to plot HOW FAR OUT OF EQUILIBRIUM the water will be at various levels of TA and pH, it would look like the chart below.
The larger the number in the chart, the further the water is out of equilibrium.
  • Perfect equilibrium would be 0 (Zero) on this chart.
  • If the number is GREEN (<10), the pool is close to equilibrium.
  • If the number is Orange (<20) it is somewhat out of equilibrium.
  • If the number is Red (>20), there is a large pressure on the water to outgas CO2 and you would see a faster rise in pH.
If your pH rise is rapid and difficult to reasonably manage, reduce your TA to the point your pH rises at a rate that you CAN reasonably manage. Worry about pH (keep it in range) and pH rise (what you can manage), worry less about the absolute TA number (except to keep it at least 50).
Frameles
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