PH and TA

[fyton2v]

I know I should totally search more, but I'm not finding much info on my issue. People seem to have problems keeping PH and TA down, but I need to raise TA and lower PH.

I thought I was doing a pretty good job at keeping my pool balanced until I started seeing more and more scaling. I've realized that I haven't been watching my PH close enough. I use a Jandy SWG and I was only adding MA once a week. During this time it would shift up from about 7.4 to 7.8. Never really higher than 7.8. Anyway, I've started paying a lot more attention to CSI to keep my water steady at around -0.5 to help dissolve the scale. I'm needing to add acid every couple of days to do this. Paying attention to the CSI has caused me to pay attention to TA. I've noticed mine is at 50-60ppm. I think I should be striving for 80ppm with the SWG, but even after adding 8lbs of baking soda I can't really move the needle upwards.

So my questions:

- Keeping my PH low is keeping the TA low and I'm afraid to add more baking soda into the pool. Is there a way to bring TA up while keeping PH at 7.2?

- How much baking soda can I add to the pool before running into other issues... perhaps raising TDS beyond recommended values?

- Will doing the borates thing help any in this situation? From what I've read it seems like it may, but I really thought I could move the TA up to 80 and still keep my PH in line.

- Anyone have thoughts on the right CSI to help control scale? It's a gunite/pebble pool and I'd hate to be doing long term harm here.

Thanks everyone.

George

 

[Richard320]

Pool Calculator can crunch the numbers for you. Down near the bottom it will tell you the effects of adding chemicals. You will need to input your pool volume at the top for it to work correctly. Baking soda will raise TA without doing much to pH.

CSI close to zero will prevent scale. Conventional wisdom says ⁺/- .60 is fine. If you have high CH as I do, keep it in the negatives. My TA runs 50 - 60 and I keep pH 7.2-7.5 to offset my super high (800ish) CH. I'm also slowly lifting scale in the process. If that helps you out any.

TDS is immaterial. I've never had mine tested and my water is clear enough to toss a coin in the deep end and call heads or tails from the deck. It's just a pool store sales tactic, along with phosphates and nitrates. You already have high TDS because you have a salt pool!

 

[fyton2v]

Thanks Richard. Is there reason to be concerned about a TA of 50? My CH is around 300ppm. Originally, I thought it was higher and the main source of my scaling problem but it was really just PH creep.

 

[duraleigh]

Adding baking soda to your pool has absolutely no side affect....it simply raises your TA with just a VERY slight bump in pH. I would bring it to 70 or so.

If you keep pH, TA and CH within the suggested guidelines, you virtually never have to worry about calculating CSI.

 

[dschlic1]

There is some support to the idea that having a lower than normal TA with a SWCG will lower the amount of acid you need to add to maintain a given pH. The TA needs to be in the 50 range (perhaps lower) for this to work. I have had some small success in doing this. My problem is that the TA will raise over time, and every so often I need to reduce the TA.

 

[chem geek]

If you are dissolving existing scale, then having the pH and TA be lower is one thing, but this shouldn't be a long-term setting for you. If you increase your TA level, you are only going to be having the pH rise even faster and be using more acid to keep it down -- that is, just increasing a vicious cycle of adding acid and baking soda.

You should not need to keep your CSI so low to prevent scale. Do you have very high CH levels? If not, then doesn't a TA of 70 ppm and pH of 7.7 or 7.8 work out OK in your pool?

 

[fyton2v]

Chem geek... I can't really point to a specific reason for the scale beyond PH. My CH is around 300ppm... not bad. When I first started the pool, perhaps 9 months ago I had a TA of around 80 and I was adjusting PH downward to 7.4 or 7.6 weekly. I really stopped paying much attention to TA at that point, but for some reason it has crept downward to my current 50-60ppm now. I'm working with the assumption that using my SWG caused my PH to drift beyond 7.8 during the week. With the taylor test kit I'm using it's kinda hard to pinpoint an exact PH value when your're well into the pinks/reds. The shades pretty much look the same above 7.6. So i'm guessing it was too high over too much time on a weekly basis, otherwise why is there scale? I could be missing other contributing factors I suppose.

 

[chem geek]

When you say scale, are you referring to scale in the SWCG cell (i.e. on its plates) or on plaster pool surfaces?

So having the TA at around 70 ppm and not adding acid unless the pH gets above 7.8 and even then don't lower it below 7.6 is fairly typical with SWCG systems. Over time, the TA may drop from the acid additions at which point you can add some baking soda to bring it back up to 70 ppm.

The more advanced options (assuming you are already at 80 ppm CYA and 50 ppm Borates) would have a lower TA down to as low as 50 ppm. If that has the pH rise be slower and have you use less acid, then you can raise your CH level to compensate for the CSI. If the lower TA isn't helping with fewer and less acid addition, then there's no reason to keep the TA that low and instead use the normally recommended 70 ppm as your target.

 

[fyton2v]

It's scale buildup on pool surfaces, specifically, around my spillway. There is a lot more opportunity for evaporation there I suppose.

If you have a moment I have a method question. Using the pool calculator I need to add about 100oz of baking soda to get a rise in TA from 50ppm to 70ppm. I've been at this for over a week now and I've added at least that much baking soda and my water is still stuck at 50ppm. I've been adding perhaps 2-4lbs at a time... then managing my PH via MA the next day. A couple of days later I'd add another couple pounds. I think my method is wrong. Should I add 100oz all at once and add MA slowly to get the PH back down? Seems like everything I've read indicates that PH should come first, but I'm getting nowhere with TA and it feels like we'll eventually be swimming in soda water .

When you say scale, are you referring to scale in the SWCG cell (i.e. on its plates) or on plaster pool surfaces?

 

[chem geek]

If you are increasing TA, then you do not add acid to lower the pH. If you do, then the acid will lower both the pH and the TA. You could then just be in a vicious cycle. If the higher TA results in faster carbon dioxide outgassing and your pH rising faster so you need to add acid, then you shouldn't have raised the TA in the first place.

Try testing your TA after you've added baking soda and its mixed but before you add any acid. See if that measures what you expect. If the acid you add to lower the pH then lowers the TA back down, then you're in the cycle I mentioned above and shouldn't bother raising the TA when it hits 50 ppm.

Bottom line: don't try to raise TA and lower pH. If pH is too high and consistently rises, then your TA is too high as well. If you end up settling at a low TA level, you can always increase your CH to compensate for the CSI if needed.

 

[fyton2v]

Thanks chem geek! I'll try it with more patience this time.

 

[phipsi1237]

Fyton2v,

How did this work out for you?