My total alkalinity was 51 ppm, so I added 5 lbs of Alkalinity Increaser and month later I re-checked and my TA is now down to 26 ppm ?!

Jump to latest Follow Reply
B

bws92082

Member
Mar 12, 2022
18
San Diego, CA
The water readings were from Leslie Pools (my kit is unreliable so I rely on pros for his). I used Clorox Pool&Spa Alkalinity Increaser for Swimming Pools, 5 lb Bag, and my pool is 10,000 gallons. My understanding is that alkalinity increaser is just baking soda, so I could probably just buy some in bulk and use that instead. But I don't understand how the total alkalinity could have gone down so dramatically after treatment.

Note I also used a Calcium Hardness increaser at the same time and that level increased by 17ppm and is now at 154. Other readings are in the ideal range. Note my CYA has been increasing lately due to the tablets I'm using--it's now at 74 from 55 last month so now I guess I'll stop using the tablets and start using liquid chlorine only.

Any ideas what's going on and what I should do?
 
Last edited:
To maintain the same total alkalinity, you have to add 1.13 pounds of baking soda per pound of trichlor.

To maintain the same total alkalinity, you have to add 1.0 pound of baking soda per (2) 3" tablets of trichlor (7 ounce weight per tab).

For example, if you are going to use 6 tabs and you do not want the TA to drop, add 3 pounds of baking soda to the pool to raise the TA.
 
  • Like
Reactions: Mdragger88, mgtfp and bws92082
2C3Cl3N3O3 + 6H2O --> 3HOCl + 3OCl- + 2C3H3N3O3 + 3H+

3HOCl + 3OCl- --> 3H+ + 3O2 + 6Cl-

2C3Cl3N3O3 + 6H2O --> 2C3H3N3O3 + 6H+ + 3O2 + 6Cl-

Trichlor + water --> cyanuric acid + hydrogen ions + Oxygen + chloride.

1 mole of trichlor creates 3 moles of hydrogen ions.

232.40 g of trichlor creates 3 moles of hydrogen ions.

1 liter of hydrochloric acid (31.45% or 10 M) provides 10 moles of hydrogen ions.

1,160 grams per liter.

31.45% of 1,160 = 364.82 grams of HCL.

Molar mass: 36.46 g/mol.

This is 10 moles per liter.

300 ml of hydrochloric acid provides 3 moles of hydrogen ions.

232.40 g of trichlor is equivalent to adding 300 ml of hydrochloric acid.

8.2 oz (weight) of trichlor is equivalent to adding 10.1442 fluid ounces of hydrochloric acid.

0.5125 lb of trichlor is equivalent to adding 10.1442 fluid ounces of hydrochloric acid.

1.0 lb of trichlor is equivalent to adding 19.794 fluid ounces of hydrochloric acid.

1.0 lb of trichlor added to 10,000 gallons will lower the will lower the TA by 7.7 ppm.

50 lbs of trichlor (is equal to 7.73 gallons of 31.45% acid) in a 25,000 gallon pool will:

Raise fc by 219 ppm

Raise CYA by 133 ppm

Raise salt by 179 ppm

Lower TA by 154 ppm

To maintain the same TA, you would need to add 56.5 pounds of baking soda.

To maintain the same total alkalinity, you have to add 1.13 pounds of baking soda per pound of trichlor.

To maintain the same total alkalinity, you have to add 1.0 pounds of baking soda per (2) 3" tablets of trichlor (7 ounce weight per tab).
 
  • Like
Reactions: mgtfp and bws92082
If you want to account for the pH, 1 mole of trichlor produces 3.84 moles of hydrogen ions (Based on a pH of 7.6).

Different pH starting points will produce different pH end points.

So, predicting the exact effect of the trichlor on the pH is very difficult and it depends on the amount of trichlor added, the TA and the starting pH.

The effect of trichlor on the pH is about 1.28 times as much as the effect on the TA.

For the TA, 1.0 lb (16 ounce weight) of trichlor is equivalent to adding 19.794 fluid ounces of hydrochloric acid.

For the TA, 1.5 lb (24 oz) of trichlor is equivalent to adding 29.69 fluid ounces of hydrochloric acid.

For the pH, 1.0 lb of trichlor is equivalent to adding 25.336 fluid ounces of hydrochloric acid.

For the pH, 1.5 lb of trichlor is equivalent to adding 38.004 fluid ounces of hydrochloric acid.

2C3Cl3N3O3 + 6H2O --> 2C3H3N3O3 + 6H+ + 3O2 + 6Cl-

100C3Cl3N3O3 + 300H2O --> 100C3H3N3O3 + 300H+ + 150O2 + 300Cl- (TA).

100C3Cl3N3O3 + 300H2O --> 16C3H3N3O3 + 84C3H2N3O3- + 384H+ + 150O2 + 300Cl- (pH).

View attachment 523600

View attachment 523601

View attachment 523602
 
Last edited by a moderator:
LsiGuy said:
first off, we should start with a full test page from leslies that you have been getting. second tell us more about the pool material, it's age and what the surrounding area is like.
Click to expand...
Leslies and other pool store test results are not reliable, accurate or repeatable.
Test strips are inaccurate as well.

Most every pool store - Leslies included - uses "adjusted alailinity", which will read lower than a TA reading from one of the recommended test kits.
Test Kits Compared
 
  • Like
Reactions: Mdragger88, Saturn94 and reggiehammond
James calculation on what you need to add to offset the trichlor does not account for high TA fill water that you use.

Get a proper test kit. All this Leslies and strip discussion is junk. Not TFPC advice. Our advice is based on testing using a proper test kit.
 
  • Like
Reactions: Mdragger88 and proavia
mknauss said:
Get a proper test kit.
Tablets are very acidic. You must add baking soda to counter act that.
Click to expand...

proavia said:
Most probably because your TA is a lot higher than you think it is and/or you have lots of aeration.
Click to expand...
I did notice on the recent test results there is an asterisk next to the TA 26* which indicates: "Total Alkalinity has been adjusted due to the effect of CyA on tested Total Alkalinity". But there was no asterisk the previous month when CyA was only 55 (and TA was 51).
 

Enjoying this content?

Support TFP with a donation.

Give Support
bws92082 said:
OK, but if the trichlor tablets are acidifying my pool so much, why is the pH remaining relatively constant at 7.6?
Click to expand...
The pH is probably not as stable as you think.

You do not have good test results that are accurate and reliable.

The pH can remain stable if the TA is high enough or if you add baking soda as needed.

Bicarbonate creates carbon dioxide and the carbon dioxide increases the pH as it comes out of the water.

In any case, get a good test kit and test regularly so that you have accurate and reliable data to work with.
 
  • Like
Reactions: bws92082
What makes you think that the people who work at Leslies are "the pros"?
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply