Another Request for TA level before adding Borates

[BassTrix]

In reading a recent thread of same topic, it appears that appropriate TA level may be determined on a case by case basis.

In the recent past, I have been maintaining TA between 60 & 70 which corresponded to a pH range of 7.5 to 8. This required ~16oz of MA every 3-4 days.

More recently, I've tightened up control on pH and am maintaining a range of 7.5-7.6. TA has been relatively stable at just above 60 (meaning I can just barely see a slight color shift on that 7th drop of reagent). I am adding 4oz MA every evening to maintain this.

My questions are:

1. Should I experiment with an even lower TA to look for more pH stability prior to adding borates?

2. What are the indications that optimum TA has been reached?


Numbers from this morning are:

FC 6.4
CC 0
pH 7.6
TA barely above 60 (I call it 62, but is more of a guess)
CH 600
CYA 75
Salt 5400
Temp 84
CSI -0.2

Thanks,
BT

 

[JVTrain]

Is there a reason why you're insistent on maintaining such a tight pH? Using your current values, if your pH were at 7.2, your CSI would be -0.57, some chance of corrosion but not major. If your pH were at 8, your CSI would be at 0.49, some chance of scaling but not major. 7.4 to 7.8 would be -0.4 to 0.3. That would be fine as well.

The optimum TA is the case were you have to add acid as infrequently as possible. Let your pH hang at 7.8 as long as you can until it's actually over 7.8, then bring it down to 7.4-7.5, in my opinion. At higher pH levels, the carbon dioxide outgasses slower so lower pH rise, less acid usage, less fluctuation with your TA.

 

[JoyfulNoise]

You and I have very similar numbers.

You can get down as low as 50ppm as long as you target a higher pH, say 7.6-7.8. But if you want to keep the TA down there then you should supplement the buffering capacity of the water with 50ppm borates.

What is the TA of your fill water and how much aeration does your pool see each day (waterfall, spillways, bubblers, etc)? Fill water has a big effect on how low the TA will go.


Sent from my iPhone using Tapatalk

 

[chem geek]

I'd just target 7.8 as your pH and not lower below 7.6. That should use less acid. You could lower the TA if you wanted, but as was pointed out you'd probably want some additional pH buffering if you do that, but 50 ppm Borates is not free. On the plus side, the borates would prevent scaling the the SWCG cell so if the pH went too high for whatever reason it would be less of a problem for the SWCG.

 

[BassTrix]

Is there a reason why you're insistent on maintaining such a tight pH? Using your current values, if your pH were at 7.2, your CSI would be -0.57, some chance of corrosion but not major. If your pH were at 8, your CSI would be at 0.49, some chance of scaling but not major. 7.4 to 7.8 would be -0.4 to 0.3. That would be fine as well.

The optimum TA is the case were you have to add acid as infrequently as possible. Let your pH hang at 7.8 as long as you can until it's actually over 7.8, then bring it down to 7.4-7.5, in my opinion. At higher pH levels, the carbon dioxide outgasses slower so lower pH rise, less acid usage, less fluctuation with your TA.

The pH recommendation comes from this thread: Will high Ca Level Reduce SWG Output?

Trying to optimize the efficiency of SWCG.

- - - Updated - - -

I'd just target 7.8 as your pH and not lower below 7.6. That should use less acid. You could lower the TA if you wanted, but as was pointed out you'd probably want some additional pH buffering if you do that, but 50 ppm Borates is not free. On the plus side, the borates would prevent scaling the the SWCG cell so if the pH went too high for whatever reason it would be less of a problem for the SWCG.

Fill water TA is ranges from 90-130 taken at various times of the year. This time of year it's running at 120. Aeration is minimal. I rarely run the waterfall and returns point downward. About the only aeration comes when a floor pop-up is pointed right at the wall in shallow end.

- - - Updated - - -

I'd just target 7.8 as your pH and not lower below 7.6. That should use less acid. You could lower the TA if you wanted, but as was pointed out you'd probably want some additional pH buffering if you do that, but 50 ppm Borates is not free. On the plus side, the borates would prevent scaling the the SWCG cell so if the pH went too high for whatever reason it would be less of a problem for the SWCG.

Yes, I'm planning at add 50ppm borates...just want to know if I should adjust TA lower than 60 (where I've been running it) or if I'd be better off running it at some lower number. The 7.5 pH recommendation was based on the high CA level in my pool (600).

 

[JoyfulNoise]

Yup, I think you've been stealing pool water from me as those numbers are dead on to what I have

With that fill and minimal aeration, I'm going to say you can get to 50ppm TA with a good bit of work (ie, adding lots of acid to drop the TA) or just let it hang where it is at 60-70ppm. With your current TA and 50ppm borates, I'll wager you'll be able to hold your pH at 7.6-7.8 for a 7-10 days easily.

I add about 12oz of MA every 7 days or so and my water stays in the 7.6-7.8 range. I have 50ppm borates and ~65ppm TA currently. I have never seen any white scale in my SWCG and my tile has no scale on it except for a very small patch near the waterfall where the water is very splashy.

My advice to you would be to keep it simple as possible. Trying to go too far down in TA is just as much work as trying to keep pH at a specific value. If you fluctuate around the TFP recommended ranges, your pool water will be just fine.


Sent from my iPhone using Tapatalk

 

[BassTrix]

on Wednesday afternoon I dumped ~1/2 cup of white flakes out of the floor drain sock! pH was 7.6 and CSI was -.2. Is it normal to accumulate that much CA when pH is at that level? Borates to be added very soon.

 

[chem geek]

Usually not that much when the CSI is kept slightly negative, but if that's all from the SWCG then the borates should help considerably since it cuts down the pH rise roughly in half at the hydrogen gas generation plate.

Is your flow rate on the low side close to the minimum the SWCG desires? A slower flow rate would have the pH rise more in the SWCG cell. Your signature implies a single speed pump so I wouldn't think that would be a slow flow rate.

 

[BassTrix]

Usually not that much when the CSI is kept slightly negative, but if that's all from the SWCG then the borates should help considerably since it cuts down the pH rise roughly in half at the hydrogen gas generation plate.

Is your flow rate on the low side close to the minimum the SWCG desires? A slower flow rate would have the pH rise more in the SWCG cell. Your signature implies a single speed pump so I wouldn't think that would be a slow flow rate.

Based on the pump curves, filter pressure, and vacuum level at the pump, I should be flowing about 95GPM.

I wish my controller had an adjustment for reversing polarity. I haven't been able to determine the cycle, but it doesn't change each time the pump & SWG turns on.

I added most of the boric acid today...waiting on the strips to top it off. Looking forward to a more stable pH and cleaner SWCG!

 

[chem geek]

Usually they change polarity every 2 or 3 hours of ontime, but it varies by manufacturer. They want it to be fast enough to not build up too much calcium carbonate but not so fast that they wear out the plates faster since changing polarity puts stress on the plate coatings (though I've only heard that and never seen technically exactly what is going on that is "stressful").

 

[JoyfulNoise]

Usually they change polarity every 2 or 3 hours of ontime, but it varies by manufacturer. They want it to be fast enough to not build up too much calcium carbonate but not so fast that they wear out the plates faster since changing polarity puts stress on the plate coatings (though I've only heard that and never seen technically exactly what is going on that is "stressful").

My guess would be hydrogen stress embrittlement.

There is a method of doing a thin nickel coating in stainless steel prior to doing electroless nickel deposits called "nickel striking". The nickel strike bath is nothing more than a solution of nickel chloride and hydrochloric acid. The plating current has to be very high and there's significant quantities of hydrogen gas generated at the working part during the initial anodic cleaning step. The counter electrode is usually a Pt mesh. You can only do a thin Ni coating (sub micron) because hydrogen gas incorporation can embrittle the Ni film. This is not a problem since the second step, electroless Ni, just needs a very thin Ni surface to deposit on and then it goes on it's own.

I bring up hydrogen embrittlement and stress cracking because I think some of the transition metals used in the SWG plate coating have appreciable hydrogen solubility.

Just a theory....


Sent from my iPhone using Tapatalk