To Run Alow Ta, Or Not To?

[Jeff F]

As has been explained before (Thanks Chem Geek), a lower TA can mean less frequent additions of HCl, when using liquid bleach as the sanitizer. (The bicarbonate buffer system, eventual offgassing of the CO2, resultant increase in pH, requiring addition of H+ ions to restore pH to normal for a pool, in short.)

I have found that by keeping my TA in the range of 55-60, I have to add acid much less often. Really quite a difference. Of course the downside is a bit of a decrease in my CSI, but it's still in the range of -0.45. (Plaster pool, and I have about 25ppm borates - kept low because of my thirsty dogs.)

This is really more convenient re. adding HCl than keeping the TA in the traditional range of 70-120.

My question is: Other than the hit on the CSI, is there any downside to running the TA a bit low, around the 55-60 range? My pH seems plenty stable this way.

Edit- title should read "a low TA" not "alow Ta" but apparently I can't edit that part.

[quantumchromodynamics]

For plaster, it is very important to avoid a negative CSI. What pH are you trying to maintain? If your TA is only 60 ppm, then you are probably trying to maintain a pH below 7.6.

I recommend a pH of 7.6 to 7.9. Using a higher pH range will allow you to maintain a higher TA. Once you get your pH and TA in the range you are happy with, you should increase your calcium hardness to achieve at least a 0.0 CSI.

What are all of you readings?

pH

TA

Calcium

Cyanuric acid

Borate

Temperature

[Jeff F]

I am trying for a pH of 7.6 on average, with occasional excursions permitted 7.3-7.9.

From my Taylor 2006 kit today:

pH 7.6

TA 60-65

CH 280

CYA 65

Borate 25

67F

FC 4

CC 0 (The chlorines being measured to precision of 0.5ppm)

Volume 25K gallons

Environment: Imagine this 25,000 gallon pool dropped into the TV series "Little House On The Prairie." Rural, with prevailing wind blowing all sorts of native grass pollen/seeds just to land in my swimming hole. And it sparkles since I've read this forum, and another forum too.

[waterbear]

bring your calcium up to around 400 ppm and then don't lose any more sleep over it. Also, make 7.6 the LOWEST you keep you pH. 7.7 or 7.8 s fine. when it climbs above 7.8 then lower it to 7.6 and not lower.

[quantumchromodynamics]

I don't necessarily disagree with waterbear; I just have a slightly different opinion about where the best place is for the levels. I think that the best place for the pH is 7.8 to 7.9. I wouldn't lower the pH to less than 7.8. I don't lower pH until it gets to above 8.0, and I rarely need to lower pH. A higher pH will also help prevent metal corrosion.

At that higher range for the pH, you should see that your TA is higher as well. Once your pH stabilizes at 7.8 to 7.9, you should increase your calcium to get your CSI out of the negative range. I think that I would try to keep the calcium below 300 ppm.

Because the temperature affects the CSI, you should anticipate the effect that upcoming temperature changes will have on the CSI. One reason I recommend a lower calcium level than waterbear is that as the water warms up in the spring, the calcium level is the hardest thing to adjust to lower the CSI. The pH and TA are easier to lower, if necessary. My recommendation for the CSI is between 0.0 and +0.3 for plaster.

You have some leeway in where you keep the levels. The main point is to avoid a negative CSI. You will have to find the optimum levels for your pool and what works best for you.

[chem geek]

From personal experience, the main problem with targeting a higher pH is if you've got metals in the water since a pH getting towards 8.0 or so can precipitate staining (actually, even lower pH can as well, depending on metal concentration). With the iron in my pool, I shouldn't go above 7.8 or else I can start to see some yellow staining. I normally target closer to 7.5, but I have a pool cover that limits outgassing.

There are many different ways to handle this and certainly adding CH or raising pH or some combination of the two will compensate for the lower TA.

[quantumchromodynamics]

That's a good point about the possible staining. For situations where scaling is a risk, such as waterfalls and SWGs, I think that trying to use a higher pH and a lower calcium level can be beneficial. I also think that a higher pH will help prevent metal corrosion.

[Jeff F]

Thank you all very much for the helpful advice.

No metals in the water as far as I have been able to detect (at least since I stopped using the D@^^%#d copper products - green hair got old quickly).

The big picture good news is that I now have the time to contemplate relatively minor issues like this, rather than running around in circles trying to control algae outbreaks, and so on.

So, thanks again!