Optimal TA with 50 ppm Borates

[davethomaspilot]

I was using lots of muriatic acid to keep my ph balanced (relatively new plaster pool). So, I took the advice on this forum (JoyFulNoise, I think) and went with a lower Total Alkalinity. That helped a lot! Muriatic acid usage was reduced dramatically.

I suppose the PH wasn't "buffered" as much, but that didn't turn out to be a problem with the automatic dosing that Intellichem provides.

I decided to give Borates a try and added enough Boric Acid to target 50 ppm. I'll check it after after the recommended 48 hours has elapsed.

Is there any reason to go to the recommended 70 ppm TA, if I don't have a problem maintaining PH balance?


In case it's relevant, I don't use CYA, so I'm likely running shock level of FC all the time, according to the graphs with zero CYA. But, we haven't noticed anything like irritation or harshness.

I don't want to open up that discussion again, but I do want to know if it changes what TA I should target given 50 ppm borates.

Thanks!

 

[JoyfulNoise]

Hi Dave,

TA in general is composed of several components, basically anything that can accept a proton (H+). For pools, the main components are carbonates, cyanurates and borates. If you want to get deep into the chemistry weeds on the topic of pH buffering, see this post -

pH Buffer Capacity

Basically, if your pH stability (acid demand) is to your liking with your current TA, then there's no need to drive it further. Depending on the TA of your fill water and your evaporation rates, trying to drive it down further may be a futile effort. As you've mentioned, give the borates a chance to work with your acid dosing system and see how things go. Borates are more effective buffers against pH rise and many popols with borates will hang in the 7.7-7.9 pH range for quite some time. So if you set your pH target for your acid dosing system a little higher, you may find that it has to run very little.

I forgot, are you still using the copper ionizer or have you pulled that out completely? Let us know how your low CYA/low FC experience goes. Most people don't have automated chlorinating systems, so it's always good to see how those systems operate in real world pools as opposed to what the marketing literature says.

Best of luck

 

[davethomaspilot]

Depending on the TA of your fill water and your evaporation rates, trying to drive it down further may be a futile effort.

Actually, I am always having to add baking soda to get TA up, even when targeting relatively low values like 40 ppm. But, I decided shooting for 70 ppm just meant that more acid was needed.

I could definitely tell the PH moved more easily, but as I mentioned, the automatic acid dosing made that a non-issue.

I forgot, are you still using the copper ionizer or have you pulled that out completely?

I turned if off. I haven't measured copper since my posts of last summer.

I've had excellent results with using 0 CYA and Intellichem for chlorine and acid dosing.

I was going to see if I could measure FC depletion versus CYA in direct sunlight at low CYA levels, but I didn't get that done.

Recall that theory says you will use less chlorine at low CYA, but some anecdotal evidence suggests other "shading" effects may be important.

My actual chlorine use is much more sensitive to temperature than amount of direct sunlight. But, as you pointed out, that maybe because the dosing is based on ORP, not actual FC. So, maybe temperature is affecting the ORP sensor.

I do know that my pool's FC depletion is negligible with 0 CYA in cool, sunny, weather. But, you suggested that might be due to residual copper in my pool.

Anyway, it's been all good. I had one mysterious incident when I added a lot of well water to the pool to cool it off. The well water caused a temporary green tint to water), but other than that I'm on year two with no issues at all and only having to fill the acid and chlorine containers very couple of weeks.

 

[JoyfulNoise]

The muriatic acid is what is lowering your TA. Your system doses acid, that lowers the pH and TA, and then aeration and natural outgassing of CO2 from the water raises the pH back up. Then the dosing system adds more acid and ... rinse, lather, repeat. Over time, and with no additions of baking soda, the acid dosing system would lower the TA to dangerously low levels and make the water very corrosive towards plaster (as measured by the CSI).

What pH value are you shooting for?

 

[davethomaspilot]

7.6 PH

According to the Pentair App, 7.4 is ideal at TA=70, Calcium Hardness = 330, and CYA = 0. 7.6 is "normal", not scaling.

 

[JoyfulNoise]

7.6 PH

According to the Pentair App, 7.4 is ideal at TA=70, Calcium Hardness = 330, and CYA = 0. 7.6 is "normal", not scaling.

Yeah, the Pentair app is using the Langlier Saturation Index (LSI), TFP prefers to use the CSI (calcite saturation index) as it is based more on the direct chemistry of calcium carbonate scaling versus the LSI which has a lot of approximations that are not derived from first principles but just added in to "make the numbers work".

See here for another in-depth discussion - Langelier and Calcite Saturation Indices (LSI and CSI))

A pH of 7.6 is fine. Given your low CYA values, the CSI is going to hover mostly around 0 so you're ok with respect to saturation. The only concern is the constant need to add bicarbonate which is an artifact of the acid dosing system. If the pH were allowed to climb to 7.8 before any dosing occurred, and then only lowered to 7.6, there may be sufficient build up of bicarbonate from the fill water to hold everything fairly stable. In my own pool, the sweet spot is to let the pH bounce between 7.6 and 7.8 and that keeps the TA mostly stable at around 60-70ppm. Since my fill water adds alkalinity to the pool, the amount of acid added to maintain the pH range is enough to keep the TA right at that level. If I try to force the TA too low, it's just a waste of acid.

 

[davethomaspilot]

Ok,

I can certainly change the PH set point to 7.8, but I don't recall the ability to set something like "dead band" so that it doesn't bother dosing until ph gets below 7.6.

I can probably do it indirectly, since I do recall configurable parameters that define the maximum dose and how much (if any) to change the max dose as PH approaches the set point.

But, acid usage since last fall hasn't been an issue. I just figured it would go back to being an issue if I kept 70 ppm TA (or higher) instead of the 40 - 50 ppm I've been using since your suggestion to try lower. Since the instructions on how to try borates said start with TA = 70, I just wanted to make sure I was going to be ok if I stayed where I've been.

Thanks!

 

[JoyfulNoise]

Good to hear. It sounds like you've got a good handle on all your chemicals and you're in a good spot. You're definitely making all the right assumptions so I say keep on doing what you're doing and should be in for another great swim season.

Thanks for posting back your results with your automation setup, it's always good to get other reference points.


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[ny2nc]

Hi there! I have absolutely nothing useful to add to this conversation, but I saw you were in little old Apex, NC as well! Just wanted to say "Hi!" to a local!

I was using lots of muriatic acid to keep my ph balanced (relatively new plaster pool). So, I took the advice on this forum (JoyFulNoise, I think) and went with a lower Total Alkalinity. That helped a lot! Muriatic acid usage was reduced dramatically.

I suppose the PH wasn't "buffered" as much, but that didn't turn out to be a problem with the automatic dosing that Intellichem provides.

I decided to give Borates a try and added enough Boric Acid to target 50 ppm. I'll check it after after the recommended 48 hours has elapsed.

Is there any reason to go to the recommended 70 ppm TA, if I don't have a problem maintaining PH balance?


In case it's relevant, I don't use CYA, so I'm likely running shock level of FC all the time, according to the graphs with zero CYA. But, we haven't noticed anything like irritation or harshness.

I don't want to open up that discussion again, but I do want to know if it changes what TA I should target given 50 ppm borates.

Thanks!

 

[davethomaspilot]

Hi back to ny2nc! I'm not getting email on new posts and hadn't checked back on this thread.

I must have added too much boric acid, since the test strips say I have 80 ppm borates.

What's the downside of having too much? Should I drain water immediately, or just let it decay due to normal backwashing and rain overflowing?

 

[JoyfulNoise]

You're fine. You would need to up near 300ppm before there was ever any concern. I would just leave it where it is and let natural decay from backwash/splashout/rain overflow dilute it away.


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