?What happens to all the acid?

[chem geek]

Pools are intentionally over-carbonated and the equilibrium amount of TA in water of pH 7.5 with no CYA is only 10 ppm (with 30 ppm CYA, it would be a TA of around 20 ppm). However, in practice, the pH tends to be stable with a TA somewhere in the range of 50 to 80 ppm depending on the amount of aeration or turbulence in the pool. With a pool cover, the TA can be much higher and not see a rise in pH.

So the real answer is "it depends" since it is very dependent on the amount of air-water exchange. Those with fountains, waterfalls, spillovers, frequently splashing kids, returns turned up, aeration jets, etc. will tend to see a lot of pH rise. Those with saltwater chlorine generators (SWG) will also see a rise though this may be partly due to some loss of chlorine gas that doesn't get dissolved in the water so lowering the TA helps but not as much as in non-SWG pools.

An extreme case of this effect is described by one pool user here. Note that you do not want to use a low TA if you are using an acidic source of chlorine (Trichlor or even Dichlor which is actually acidic when accounting for chlorine consumption) but should only consider a lower TA when using hypochlorite sources of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite). Also, if you have a lower TA, then you may need a higher pH and/or CH to compensate so that the saturation index is near zero.

In addition to a lower TA helping to reduce the rate of rise of pH, a higher pH target also helps. This chart shows the relative rate of carbon dioxide outgassing at various TA and pH levels. HOWEVER, this assumes a linear relationship between dissolved carbon dioxide level and outgassing rate when in fact it appears that the rate is proportional to the square of the TA due to some facilitated transport effect (according to Wojtowicz).

Richard

[Vetsa]

Thanks for all the info Richard. Now I have my TA level down the PH is not rising much, it's great not to add so much acid all the time

It's swimming season here now so have been enjoying swimming in the pool instead of just looking after it.

thanks again

[chem geek]

Glad it's working out for you. You should use The Pool Calculator to calculate your saturation index (don't forget to include the salt level) and if you have a plaster pool then you may need to raise your Calcium Hardness (CH) or your target pH some so you are closer to zero since your lower TA will lower your saturation index if you don't compensate with one or more of these other factors. You don't have to be exactly zero, but I wouldn't go below -0.2 as a long-term target if you can help it.

[Guest]

Thanks again Richard, I get it now.
Another question, I'm a pain aren't I. The pressure gauge on my filter is very low, I have replaced my gauge but it's still low. The whole pool system has only been installed for about 7 months. Could it be the imperella being partly blocked? Everything sounds okay and looks to be working okay.

the pressure should be low if its higd it's time to clean the filter 2psii is good 10 or above needs to be clean