Confused about total alkalinity vs. carbonate alkalinity

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New2PoolsInAZ

New2PoolsInAZ

Member
Jul 13, 2019
16
Sun City, AZ
I am brand new to pools and had our 14.5K gallon Pebble Sheen pool just finished this April. I am very new at this but have read quite a bit. I am using 99% Trichloro-s-trianzinetrione in a deck chlorinator which I understand adds to CYA levels. I just started using liquid chlorine to shock. My current CYA level is already between 90 and 100 ppm. Recommended alkalinity for a Trichlor pool is about 100-120 ppm from what I have read. My alkalinity is at 120 ppm so that seems to be good though some may suggest to lower by 10 ppm.

My Taylor 2006 test kit booklet has a section called Cyanuric Acid Correction to Total Alkalinty which reads "Since water balance calculations only use the carbonate alkalinity portion [of total alkalinity] a correction (which varies with pH) should be applied to compensage for the cyanurate portion [of total alkalinity]." The calculation basically says to take 1/3 of the CYA level (100 in my case, so 33) and subtract that from the Total Alkalinity (120) which gives me 87 ppm alkalinity. This is reiterated at
Cyanuric Acid: Good or Bad? - Taylor Technologies Pool - Medium which states "the total alkalinity titration measures both carbonate and cyanurate alkalinities. This affects water balance calculations because the alkalinity term in the Saturation Index equation is strictly carbonate alkalinity. So high CYA levels can lead you to think you have the proper or high carbonate alkalinity levels. To determine the true carbonate alkalinity value, subtract one-third of the CYA reading from the total alkalinity reading."

I have searched all over the place trying to determine if the ideal 120 ppm (or some say 100-120 ppm) for alkalinity for Trichlor pools needs to be adjusted for my CYA. It makes a huge difference in my case as I may only technically have 87 ppm Trichlor in which case I want to increase at least to 110 ppm. Every product I come accross to raise or lower alkalinity says nothing about adjusting for CYA levels. So either the manufacturers of these products are not telling me something I need to know to properly balance my pool, or Taylor is incorrect. Being new though I don't think either of this is possible and I am missing something. Any thoughts?

Thanks so much!

John
 
Welcome!

A couple of things:

- Regarding your immediate question - the common discussion here is that while you need to know the TA to have a good understanding of how chemicals meant to adjust your pH will do so, and that you need to have above a certain level to avoid rapid pH swings, you don’t need to aim for a specific TA. It will balance out over time. Acid will reduce it as it reduces the pH.

- Trichlor is very acidic and thus the pH is more stable when the TA is higher. If you chlorinate with something like say liquid chlorine, which is effectively pH neutral, your pH will rise over time as no acid is being added by the chlorination method. So TA can be much lower to avoid it.

- Now the million dollar point: the advice you get here is VERY different from what you will get elsewhere. This forum and site acknowledges the buffering effect CYA has on active chlorine. Your CYA is very high, and your FC levels will need to be commensurately high. The advice you get here is going to be a different methodology from elsewhere. We feel it is superior as it gives you more control over your chemical levels, you know exactly what the effects are of the chemicals you add, and the chemicals are readily available from multiple sources and not just from a pool store that is looking to potentially have you dump things in your pool that won’t actually help, with the intent of selling you things. I highly recommend you try the methods here out, but to do so you will need to exchange about half of your water and switch away from chlorinating with trichlor and chlorinate with liquid chlorine instead.
 
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Thank you. I realized after posting then reading another newbies post that TFP had a system it's expected one to understand. I started reading two of the articles in the Pool School and want to continue doing that. Once done I will post again! As I just got this pool, and it's my first, I do want to move away from TriChlor and perhaps I will indeed do it the TFP way, just want to read more first. Thanks again for being there!
 
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I would read the pool school articles and some of the recent large threads of people who had trouble with their pools. It sounds like yours is looking good, but with a CYA of 90-100 it will go sour at some point unless your FC stays so high that you will have a hard time testing your pH accurately.

I just started being a pool owner about 3 months ago, and now I have a beautiful pool and spend maybe $5-10/wk in chems to keep it that way.
 
I am going to start using the TFP methods but am still learning. I will start using liquid chlorine and not the Trichlor I started with. Right now I am both draining and filling my pool with fresh water at the same time (so to not damage the pebble sheen in the hot sun) and by doing this will lower CYA to 40 or 50. It may be covered in something I've not yet read (there is a lot) but is there a good target TA I should set the new water in the pool at before adjusting PH? Note I live in Phoenix and the outside daily temperatures run now between 105-115 degrees and the pool water between 92 and 94 degrees, not sure if that matters.

And given I am in Phoenix, is 50 or 50 a good CYA level to have? I read in some posts to keep it higher in Phoenix, someone even said 60. The pool is in full sun all day, no shade at all.

Thanks!
 
If TA is below 50, add either baking soda (if pH is adequate or high) or soda ash/washing soda (if pH is low) to get to 50.

If TA is high, like 90+, you really don't have to focus on adjusting it - just adjust your pH. If you're chlorinating with liquid chlorine as recommended, high TA will pull your pH up. If you adjust it back down with acid, it will lower the pH and take a little of the TA down with it each time. Eventually the TA will be low enough that the pH rises will be further and further apart.

50 CYA sounds good for Phoenix, so long as you don't currently have an issue that needs you to keep the FC levels high (SLAMming the pool). You can do a SLAM at 50 CYA if need be, but it will use more chlorine. I'm imagining your water is likely pretty pricey there? If so, keeping CYA at 50 is probably best even if you have to SLAM. You'll just have to use more chlorine, but that might not be so bad as changing out more water would be.
 
I think I confused TA and CYA in one part of my post just above this (sorry, very new). But you gave me what I need, 50 CYA is good for me in Phoenix For TA, I will only raise TA if it's below 50 and otherwise depend on my adjustments to PH. Thanks again for the advice. I'll soon be reading more in the pool school.
 
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If you're not having any issues with the water, just test FC daily and add chlorine. After a while you get a feel for how much you're using and can cut the testing down to 3-4 times a week. Still need to add daily, though!

I recommend putting your pool info in your signature - that will help us later if you need more advice. :)
 

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CarolD said:
Woah, I am so confused. Everything I've read says liquid chlorine has a PH of 13. How can that be considered neutral?
Click to expand...
When it goes through the process of sanitizing the pool water, the overall action is pH neutral.
 

Key Misunderstandings and Problems in Pool Water Chemistry (Part I)

How much chlorine does a pool need? How can I quickly balance water? Why is the pH always going up? A chemist answers these questions and more.
aquamagazine.com aquamagazine.com

Liquid chlorine does not raise pH. When added to water, liquid chlorine (which has a pH of 13) makes HOCl (hypochlorous acid – the killing form of chlorine) and NaOH (sodium hydroxide), which raises pH. But when the HOCl is degraded by UV, and when used in killing and oxidation, it creates HCl (hydrochloric acid). The amount of HCl is almost identical to the amount of NaOH. So the net effect on pH is zero (or almost zero).
 
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