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.
If you have a question about any information within this Sticky, please start a new thread for yourself where you will receive very quick responses to your specific questions. Thank you! Introduction There are two main things to consider when maintaining your hot tub water, Water Balance and...
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.
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.