Chlorine Bleach & pH

[SnoopysGirl]

I am sorry if this question has been answered in the past. I did look through the forum late last night and didn't find exactly the answer I was looking for.

Since starting to use liquid chlorine in the pool, my pH and TA have been rising, as I would expect. When should I lower it? Do I need to lower it, or will it eventually stabilize on its own? Here are my current readings for pH and alkalinity, taken today with the Taylor K2006:

pH 7.6 (not too bad, but on the 17th of July was 7.4 - has been rising steadily since)
TA 220 (adjusting for CYA 130 - TA was 190 on the 11th of July)

[waterbear]

The reason your pH is rising is because of your high TA. Bleach will not cause TA to rise. Adding baking soda or pH up will. When using unstabilized chlorine such as bleach (or cal hypo or lithium hypochlorite) which are all basically pH neutral on use you need to lower the TA to around 80 to 100 ppm. Even for acidic chlorine sources such as trichlor and dichlor are better off is the TA is no higher than 150 ppm. The pH is rising because of outgassing of CO2. Adjusted TA is a measure of the bicarbonate in your water. The higher the bicarbonate the faster CO2 outgasses and the faster pH rises. Read the sticky on lowering TA and follow it.

Also, the lower you put the pH the faster it will rise so don't drop the pH below about 7.6 and wait for it to get close to 8.0 before you lower it.

If your adjusted TA is 220 then you are bound to have pH stability issues! What is the TA of your fill water?

[SnoopysGirl]

When I look in the instruction manual in the Taylor kit, it says that liquid chlorine has a pH of 11-13 and has a high acid demand. I am confused - I thought that adding 10% liquid chlorine would raise the pH & TA. I haven't had a problem like this before using the liquid chlorine. I read through the sticky - so I should aerate and add muriatic acid to lower TA? I will test fill water in a bit.

[PoolDoc]

Ignore that dumb book*. It's wrong! That nutty thing was one of the reasons I started making my own kits (and still would be, if I was a better business man).

I ran a 300,000 gallon public pool with hundreds of swimmers, on straight industrial 15% bleach for THREE years, and never used a single bit of acid!

-- You can use the ABD tables, if you like --

*There is a reason why the book says what it does, and there's a reason why it's wrong in practice but the explanation runs to very long.

[SnoopysGirl]

Okay, so what you are both essentially saying is that my fill water is likely the problem, & probably the reason I wasn't having pH and TA issues BEFORE switching to liquid chlorine is because of the acidity of the trichlor tabs I was using? Ben, the ABD tables - are those the ones in the Taylor book? Sorry, I am not familiar with ABD tables. Let me know if there is a link I am missing.

[PoolDoc]

ABD => Acid / Base Demand.

Using trichlor with high alkalinity fill water would tend to compensate for the pH issues with the water. Bleach, used routinely, has almost no impact on pH or TA. When you FIRST add a dose, it does raise both somewhat.