Why keeping alkalinity so low with bleach method ?

ItsUncleBob

Active member
Aug 22, 2020
42
Buffalo NY
Hi Guys,

Could someone educate me place!

All literature online says optimal hot tub alkalinity is 80-150 with Ideal 120....

I see here 40-50 alkalanity, wouldnt that create issues with pH bounce

Thank you
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
The"all literature online" you are referring to is probably generic pool industry standard ranges just like for pools. It's just that - generic, and does not take into account all chlorination methods, surface types, etc. WIth an acrylic tub, there are no concerns for eroding plaster or a low CSI, so the main concern is pH fluctuation. Since we know tubs have a pH that tends to jump quickly due to aeration, a lower TA generally helps keep the pH from skyrocketing too fast. A TA of 40 is a bit low, but 50 should be fine. You can read more about those levels in the link below. Hope that helps.

 

JoyfulNoise

TFP Expert
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May 23, 2015
17,445
Tucson, AZ
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Nope. pH “bounce” is just more pool industry pseudoscientific sounding nonsense.

The pH rise in your hot tub is the direct result of the outgassing of dissolved CO2. Your TA is, primarily, carbonate alkalinity. The lower your TA, the less dissolved CO2 there is in equilibrium. The lower the dissolved CO2 concentration, the less driving force to outgas. The less outgassing of CO2, the slower the pH rise.

Increasing alkalinity just means you have to add more acid to move the pH. You’re tub water is perfectly safe with any alkalinity down to about 40-50ppm.

Bleach is a fairly neutral pH chlorine source. Therefore you don’t need high TA to offset the acidity of dichlor or other acidic sources of chlorine.
 
Last edited:

ItsUncleBob

Active member
Aug 22, 2020
42
Buffalo NY
Dang... I just freaked out after running the CSI and LSI calculators and started raising my ALK

I was at

60 ALK
pH 7.5
CH 125-150

It told me that my water was corrosive ... Was afraid of damage to the tub.

Question, why does alkalinity drop by itself... I started with 120 and after 3 weeks it was at 60

Thx guys
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,445
Tucson, AZ
Pool Size
16000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Adding acid reduces TA. TA and pH are not independent of one another. Both dichlor and trichlor (not really used in hot tubs) are acidic and will reduce TA. Dry acid is sodium bisulphate and it reduces both TA and pH. Muriatic acid reduces TA and pH. Bleach will initially raise pH and increase TA slightly but the sanitation and oxidation reactions of chlorine are acidic in nature and so pH and TA will decrease as the chlorine is used up. Your fill water may be high in TA and so it will raise TA as you add it.

This is why self-testing regularly is important as anything you add to the tub (including yourself) will change the chemistry.
 

ItsUncleBob

Active member
Aug 22, 2020
42
Buffalo NY
It all makes sense, thank you

My intial fill water
pH 7.1-7.2
ALK 80-90
Total Hardness: 80

I will be running some AHh Some and dumping water...

I will add some dichlor as soon as I fill the tub ( whole house catalytic carbon filter, my taps at not detectable chloramine levels )

Then I will add some calcium.

I will leave Alk as is

pH i will raise by running jets.

Does this sound like a good strategy?

Thank you
 
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