I've noticed over the past couple of full tests that my TA is rising...could be tester error, but I don't think so. See numbers in my sig, along with what I add each day; as you can see, the only thing I've been adding since we went SWG is stabilizer or Muriatic Acid...if anything, I expected my TA to lower more, not raise.
Why is my TA rising?
- Thread starter gilbee
- Start date
Since I see that you replastered this year, it's not uncommon for TA to rise as the pool surface continues to fully cure. Carbonate compounds can and will leech out of the pool walls as it continues to cure, raising TA. CH will likely rise for the first year as well until everything fully cures.
Keep dosing with acid and dropping your pH to 7.6 or so when the pH rises.
Keep dosing with acid and dropping your pH to 7.6 or so when the pH rises.
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I would agree with new plaster you'll see some TA rise. Otherwise it can increase through evaporation and refill. How much depends on your fill water TA.
- Dec 23, 2014
- 163
- Pool Size
- 14000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Jandy Aquapure 1400
its strange that your TA is rising especially for how much acid you are adding. one thing i notice is your Ph goes up FAST and gets really pretty high. you seem to correct it by adding acid but never enough acid to get it into the 7.2 range that is usually suggested to lower TA and then use the aeration to pop up the ph again. you may want to try to really drive the ph down - i assume its the new plaster thats not doing you any favors with the high ph. whats the ta of the fill water?
Chem Geek told me over here TA balancing that I should stop driving down to the low 7s...then again, the observation I was having then was the TA was dropping quickly...maybe I need to alternate a bit. Between the SWG and the spa overflow, I get aeration and I believe that is not helping me with the pH rise, but the overflow is the only way I can reliably cycle the water in the spa through the filter...there is a drain in the spa that goes through the filter, but after playing with it a bit, I haven't been able to find an adequate partial valve position that stops the overflow but doesn't lower the water level in the spa...I should probably play with that a bit more and mark it when I find it.
It's just going to be something you'll have to deal with for the first few months/year until the plaster is fully cured. CH and TA are going to rise, with the TA rise contributing to your pH rise with SWG and aeration. Find a good deal in your area on muriatic acid and keep after it, making small adjustments to pH to the mid 7s as you need to. It will get better as the plaster cures up and good idea looking into reducing the overflow to slow down the pH rise. The other side of the coin is that your sources of aeration are forcing you to keep the pH in check and reducing the rising TA at about the same rate that it's being released by the plaster since your TA hasn't shot up that high yet. So while it stinks to be constantly adding acid, it is keeping your TA in line for the eventual day when the TA release slows/stops from the plaster.
- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I'll be a bit of a contrarian here and say that I don't think curing plaster will cause a noticeable TA rise. There are three components to plaster, calcium hydroxide, calcium oxide and tricalcium silicate (see this post and this post by chemgeek).
I won't reproduce the chemical equations here but all of the species in plaster (calcium oxide, calcium hydroxide and tricalcium silicate) absorb either water or CO2 to cure that then leaves behind a mixture of calcium carbonate, calcium oxide and silicon dioxide. The calcium carbonate should form on the surface of the plaster and become part of the silica/calcium oxide matrix. In fact, when plaster degrades and loses it's calcium carbonate layer either from physical or chemical damage, it is the exposure of calcium oxide to the pool water that drives up pH and calcium hardness. It is also true that the calcium carbonate in the surface of the plaster will be in equilibrium with carbonate and carbon dioxide in the water.
So, I think the OP's problem here is not plaster curing per se, but CSI control. If the pH is being dropped too low, then there is a greater likelihood of the calcium carbonate dissolving from the plaster surface and increasing both the calcium hardness and carbonate alkalinity of the water. This is why it is so important for fresh plaster to be in high TA water at start up and then to maintain a CSI that's a little positive - you want the calcium carbonate layer to form on the plaster surface and be as dense and thick as possible.
So my suggestion to the OP is to focus on maintaining pH in the 7.6-7.8 range and try to keep the CSI at or near 0 but allow it to be a little bit positive. If you are worried about the effects of that on your SWG, then you can also add 50ppm borates to your water which will cut the pH inside the SWG cell significantly and help prevent scaling.
I won't reproduce the chemical equations here but all of the species in plaster (calcium oxide, calcium hydroxide and tricalcium silicate) absorb either water or CO2 to cure that then leaves behind a mixture of calcium carbonate, calcium oxide and silicon dioxide. The calcium carbonate should form on the surface of the plaster and become part of the silica/calcium oxide matrix. In fact, when plaster degrades and loses it's calcium carbonate layer either from physical or chemical damage, it is the exposure of calcium oxide to the pool water that drives up pH and calcium hardness. It is also true that the calcium carbonate in the surface of the plaster will be in equilibrium with carbonate and carbon dioxide in the water.
So, I think the OP's problem here is not plaster curing per se, but CSI control. If the pH is being dropped too low, then there is a greater likelihood of the calcium carbonate dissolving from the plaster surface and increasing both the calcium hardness and carbonate alkalinity of the water. This is why it is so important for fresh plaster to be in high TA water at start up and then to maintain a CSI that's a little positive - you want the calcium carbonate layer to form on the plaster surface and be as dense and thick as possible.
So my suggestion to the OP is to focus on maintaining pH in the 7.6-7.8 range and try to keep the CSI at or near 0 but allow it to be a little bit positive. If you are worried about the effects of that on your SWG, then you can also add 50ppm borates to your water which will cut the pH inside the SWG cell significantly and help prevent scaling.
To achieve this with my current numbers and just playing with ph and adding 50ppm borates, I would have to maintain a pH of 7.9 to be slightly positive, as 7.8 would be slightly negative...that seems like a really tight line to walk if I want to stay under 8, but am targeting 7.9 to keep the CSI just over zero...what can I do to make this range that is suitable a bit wider so there's a little room to work with?
- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Please post your latest test results including TA, CH and typical daily water temperature.
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- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I would consider this an acceptable range (I bumped your CH up to the high limit of 350ppm) -
At a pH of 7.7 your CSI is, for all intents and purposes, 0. You would also likely see that the time it takes for the pH to go up to 7.9 is longer than the time it takes to rise from 7.4 to 7.6.
At a pH of 7.7 your CSI is, for all intents and purposes, 0. You would also likely see that the time it takes for the pH to go up to 7.9 is longer than the time it takes to rise from 7.4 to 7.6.
All of my historic readings are in the link in my sig, or Here
Water temp these days is in the high 80s/low 90s
- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I would think so too, I guess I got hung up on the target for positive CSI...in your screenshot, the left column is at -.12, which is not positive.
- - - Updated - - -
yes, fill water is 110TA---I haven't been adding any water though, which is what caused my curiousity. Now this morning after taking these results, I did add some water, so I expect the TA to climb a little bit, but not a major increase.
- May 23, 2015
- 24,381
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
That is true but it's not very negative either and that is a pH of 7.6. The CSI is a logarithmic scale, so the amount of calcium carbonate undersaturation at -0.1 is a lot smaller than the amount of undersaturation at -0.2. Your water would be considered "balanced" all the way up to -0.3. So, -0.1 is likely fine for your plaster. And it will only be at that value for a fairly short time as the pH will easily go up from 7.6 to 7.7 in fairly short order.
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And, if you brought your calcium hardness up to 400ppm, then the CSI would always be positive and "Balanced" (i.e., less than +0.3) between 7.7-8.0.