Suggested TA for TFP Converts

[NLITP]

So, I'm moving towards the TFP methodology and learning lots on the forum. However, I am still using trichlor tabs for chlorine at the moment (trust me... you don't want to know why). I was reading the Recommended Levels page in Pool School just now and noticed this statement regarding TA:

"if you are using trichlor tablets for chlorine, follow the above recommendations but have TA around 100-150 and be sure it doesn't fall below 100."

Can anyone explain the "...be sure it doesn't fall below 100" bit?... as in, what will happen if it falls below 100?

My current TA stays between 80 and 90. I adjusted my pH to 7.4 yesterday and today it is back to 7.6. Just curious if I need the higher TA to maintain a 7.4 pH (though I realize most would say 7.6 is perfectly fine) OR if something more serious will occur if the level drops below 100.

 

[JVTrain]

Higher TA for trichlor tab pools is recommended because trichlor is very acidic. Each tablet lowers your pH and will lower your TA over time. Every time you add any kind of acid (trichlor, muriatic acid and CYA to a lesser extent) your TA will go down. The higher recommended TA combats this constant acid addition by trichlor. Below 100 may cause your pH to drop below 7.0 with continued puck usage. If you're getting slight pH rise, as you are, your TA is likely in a good place considering the puck usage. Most people have problems keeping pH up when using pucks. It's OK if your pH rises to 7.8 or so and will likely hold their longer than it does at lower pH. Carbon dioxide outgassing (the main source of pH rise) is slower at higher pH levels.

 

[Patrick_B]

Not absolutely. It's insurance really, because Pucks used long term will drive pH and TA very low.

 

[JoyfulNoise]

Trichlor is acidic and long term use of it can cause your waters carbonate alkalinity to decrease over time. Think of it like adding acid, when you add acid your TA decreases.

Often, when people switch from trichlor to bleach, they see their pH rise more quickly and attribute it to bad bleach having too much excess lye in it. The truth is that the bulk of the waters pH rise is controlled by the amount of dissolved CO2, the pH and aeration (CO2 gas exchange between water/air). The primary source of CO2 in your water comes from the carbonate alkalinity. Therefore, when you come off trichlor, you might see a rise in both TA and pH and it might require more acid additions to keep the pH in a normal range. But you can adjust your TA lower to help mitigate that issue.


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[NLITP]

Thanks for all the answers. After reading about PH (lowering/raising), maybe my slight rise is due to my the direction of my jets. All 3 are pointing slightly left and slightly up, which causes a bit of turbulence on the surface. Should I point my jets down in an effort to keep PH from rising? I was told to have them all pointing in the same direction to cause leaves/debris to circulate around the pool and into the skimmer.

 

[BuckeyeChris]

would you rather have to skim the pool, or add 24 oz of MA every week?

 

[JVTrain]

A perfect situation for surface skimming is the jets creating a slight ripple at the surface, just enough to tell the pump is running. This will vary based on pool fill height and evaporation but you get the idea.

 

[NLITP]

Got it. Thanks guys!

 

[chem geek]

The real rule for the TA level is to set it to where the pH is relatively stable (within reason -- extreme TA can have other issues and of course the calcite saturation index may need to be adjusted via pH and/or CH). The higher TA when using Trichlor tabs is not only because Trichlor's acidity will consume TA so you want more of a buffer to prevent losing too much, but also the higher TA results in more carbon dioxide outgassing so that the pH can remain more stable.

In your case since your pH tends to rise because of the additional aeration sources you have your TA is fine or could even be slightly lower IF you make sure to maintain that TA level, say via adding baking soda.

In your 17,000 gallon pool, every 3" 8-ounce Trichlor puck will consume 2.3 ppm TA or 4 pucks consume 9.1 ppm TA. So just be aware of that and maintain the TA accordingly.

 

[NLITP]

On 7/20 at 1 PM: pH is 7.4 (due to adding MA to get it to here)
On 7/21 at 10 AM: pH is 7.6
On 7/22 at 9 AM: pH is 7.8

Nothing was added to the pool after the pH reached 7.4 on 7/20. An hour dip in the pool by the wife and I over the course of this time period was the only pool traffic. My TA has remained a constant 90 through this time period. I only have 3 return jets in the pool. None of them are pointing up so much they make bubbles... just ripples. Is it possible to have this much of a pH swing based on return jets alone?

Here is my best guess at what to try to resolve my pH rise issue:

1. Point all of my jets down (for now)
2. Add MA to bring the pH down to 7.2
3. Add baking soda to bring up the TA to over 100
4. Monitor pH daily for a few days to see how well (or not) it is holding

Other suggestions/thoughts? Thanks for all of the valuable feedback thus far.

 

[NLITP]

Great... and my pool guy just left (less than 1 hour after I tested) and left me a note saying my pH is 7.2(????). I'm using the Taylor-2006 kit and am super careful/exact with my testing. I'm testing pH again now...

 

[NLITP]

Ok... retested and still show 7.8. I turn my pump on for 5 mins before taking the sample, turn the bottle upside down, put the bottle down a full arms-length under the water in the deep end and turn the bottle over until it fills (the bubbles stop) before bringing it up. The pool guy uses guess strips, so I'm inclined to believe my results, but please let me know if you think I am doing something wrong. I would love for it to actually be 7.2 right now.

 

[JoyfulNoise]

On 7/20 at 1 PM: pH is 7.4 (due to adding MA to get it to here)
On 7/21 at 10 AM: pH is 7.6
On 7/22 at 9 AM: pH is 7.8

Nothing was added to the pool after the pH reached 7.4 on 7/20. An hour dip in the pool by the wife and I over the course of this time period was the only pool traffic. My TA has remained a constant 90 through this time period. I only have 3 return jets in the pool. None of them are pointing up so much they make bubbles... just ripples. Is it possible to have this much of a pH swing based on return jets alone?

Here is my best guess at what to try to resolve my pH rise issue:

1. Point all of my jets down (for now)
2. Add MA to bring the pH down to 7.2
3. Add baking soda to bring up the TA to over 100
4. Monitor pH daily for a few days to see how well (or not) it is holding

Other suggestions/thoughts? Thanks for all of the valuable feedback thus far.

You plan will only make your pH rise faster. You need to stop adding any baking soda. Here's what you should do -

1. Use MA to lower pH down to 7.2 and aerate your water back up to 7.8. Keep doing this until you decrease alkalinity to 80ppm.

2. Target your MA additions to get to a pH of 7.6 and allow it to drift up on its own to no higher than 8.0.

3. If your pH is still rising to quickly, then lower your TA to 70ppm and see.

By lowering your pH to 7.2 you are decreasing your alkalinity and then adding alkalinity back in with the baking soda. So you are just going in circles at this point. The main driver of pH rise in your pool is carbonate alkalinity and the outgassing of CO2. The process of of converting bicarbonate to CO2 is what consumes hydrogen ions and raises pH. As the CO2 outgasses from the water, more bicarbonate is converted to CO2 and the process keeps rolling on. CO2 outgassing rates are higher at lower pH.

Therefore you need to lower your TA and target your acid additions so that you only go down to a pH of 7.6. You lower your TA until you get to an acid addition frequency that you can live with.

 

[JoyfulNoise]

Great... and my pool guy just left (less than 1 hour after I tested) and left me a note saying my pH is 7.2(????). I'm using the Taylor-2006 kit and am super careful/exact with my testing. I'm testing pH again now...

Ok... retested and still show 7.8. I turn my pump on for 5 mins before taking the sample, turn the bottle upside down, put the bottle down a full arms-length under the water in the deep end and turn the bottle over until it fills (the bubbles stop) before bringing it up. The pool guy uses guess strips, so I'm inclined to believe my results, but please let me know if you think I am doing something wrong. I would love for it to actually be 7.2 right now.

So when do you plan to fire the pool guy? Sounds like he's not doing you any good anyway....

 

[NLITP]

JoyfulNoise.... PM sent.

 

[NLITP]

You plan will only make your pH rise faster. You need to stop adding any baking soda. Here's what you should do -

1. Use MA to lower pH down to 7.2 and aerate your water back up to 7.8. Keep doing this until you decrease alkalinity to 80ppm.

2. Target your MA additions to get to a pH of 7.6 and allow it to drift up on its own to no higher than 8.0.

3. If your pH is still rising to quickly, then lower your TA to 70ppm and see.

By lowering your pH to 7.2 you are decreasing your alkalinity and then adding alkalinity back in with the baking soda. So you are just going in circles at this point. The main driver of pH rise in your pool is carbonate alkalinity and the outgassing of CO2. The process of of converting bicarbonate to CO2 is what consumes hydrogen ions and raises pH. As the CO2 outguesses from the water, more bicarbonate is converted to CO2 and the process keeps rolling on. CO2 outgassing rates are higher at lower pH.

Therefore you need to lower your TA and target your acid additions so that you only go down to a pH of 7.6. You lower your TA until you get to an acid addition frequency that you can live with.

I am a newbie, so bare with me. I was trying to get the pH to around 7.4 - 7.6 and get my TA at or above 100 as suggested by the Recommend Levels page of this forum (remember I am still using Trichlor tabs at the moment, which states my TA should be 100+). I had the understanding that getting the TA at or above 100 would better stabilize the pH (in that sharp rises/falls would be reduced). I read elsewhere on this forum to raise TA, bring pH down a little below your target and then add baking soda to raise the TA to the target value.

You are recommending for me to bring my TA down to 80? My understanding is when you lower TA, the less stable the pH rise/fall (more prone to sharp rises/falls). So is my understanding currently reversed? Sorry for my confusion and thanks for your patience.

 

[JoyfulNoise]

I am a newbie, so bare with me. I was trying to get the pH to around 7.4 - 7.6 and get my TA at or above 100 as suggested by the Recommend Levels page of this forum (remember I am still using Trichlor tabs at the moment, which states my TA should be 100+). I had the understanding that getting the TA at or above 100 would better stabilize the pH (in that sharp rises/falls would be reduced). I read elsewhere on this forum to raise TA, bring pH down a little below your target and then add baking soda to raise the TA to the target value.

You are recommending for me to bring my TA down to 80? My understanding is when you lower TA, the less stable the pH rise/fall (more prone to sharp rises/falls). So is my understanding currently reversed? Sorry for my confusion and thanks for your patience.

How long do you plan on using trichlor pucks for? Perhaps you can post your latest set of test results (all water parameters including calcium hardness) and then we can have a better discussion.

Too often people say that they want to target a low pH like 7.4 and don't realize that there is often very little reason to do so. Either you will not be able to get that low without constantly adding acid or it may be bad for your pool to do so. Unfortunately the pool industry and pool stores tell people that 7.4 is the "correct" value (typically talking nonsense about eye's stinging and the pH of tears, etc) when the "correct" value of pH depends on a lot of other factors.

 

[NLITP]

My recent addition of MA has brought my pH to 7.4 and TA to 80. My jets are all pointing down. I'll stop and monitor for now. Thanks!

 

[NLITP]

...Perhaps you can post your latest set of test results (all water parameters including calcium hardness) and then we can have a better discussion.

Here are my current numbers

pH - 7.4
TA - 80
FC - 4.0
CC - 0
CYA - 50
CH - 200

I guess since I'm new at this, I don't really know what a "normal" expectation of my daily pH increase/decrease should be.

 

[JoyfulNoise]

Here are my current numbers

pH - 7.4
TA - 80
FC - 4.0
CC - 0
CYA - 50
CH - 200

I guess since I'm new at this, I don't really know what a "normal" expectation of my daily pH increase/decrease should be.

OK, so based on those numbers above and assuming a water temp of 88F, your calcite saturation index (CSI) is -0.31 which is just a smidgen over the -0.3 mark where it says "Potential to become corrosive to plaster". If you let your pH increase to 7.6, then your CSI is -0.12 which is considered balanced. At a pH of 7.8, the CSI is +0.08 which is, again, balanced. If you let your pH rise to 8.0, your CSI is still +0.27 which is "balanced" but very close to the "Potential to scale" limit of +0.3.

Since you live in Phoenix, you'll have no trouble getting more calcium hardness in your pool water just by topping off with municipal water BUT, if you really, really, really wanted to, you could bump your CH up to 250ppm which is the lower suggested limit for plaster. Honestly I would not bother but if you wanted to you could add calcium by switching to calcium hypochlorite for a little while.

As for acid addition frequency, if you target the lower bound of your pH to 7.6 and try to add acid only when you get up to 7.8 to 7.9, then I think you will add acid a lot less frequently. You could even drop your TA to 70ppm (with lower pH set at 7.6) and see how that works. 70ppm is just fine.

The 100ppm suggestion for trichlor comes about because most people don't realize that trichlor is very acidic and will both lower pH and TA over long periods of time. So having the extra TA helps. But, pH rise in swimming pool water is dominated by the amount of dissolved CO2 in the water and it's outgassing rate. The primary source of CO2 is your carbonate alkalinity.

So back to my first question - when do you plan to get off the trichlor pucks and switch to bleach? If your pool is not a salt pool with an SWCG, then you are already at the upper recommended limit of CYA. Phoenix is hot and sunny enough that a lot of folks can go up to 60ppm CYA and be very happy, but you're already close to the top and the trichlor adds 6ppm CYA for every 10ppm FC.