Bicarb Start-up

[bdavis466]

Ph 8.0
TA 325
Ch 125

It took 12 more ounces to drop the PH to where it is now.

I rechecked the meter and I am getting 28 gpm

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this is a cool thread. I dont recall anyone posting the test results regularly DURING their plaster start up.

Man I said it a couple times during your construction thread, but that is one serously cool pool you built yourself !

Thank you very much. I have never done a start up and no one I know of has even heard of a bicarb start up. I have always left it to the plaster guy to handle. Mr. OnBalance has been incredible thus far.

I can also vouge for Jason's pool math. It is incredibly accurate!

 

[Divin Dave]

We are extremely fortunate to have Mr OnBalance as part of TFP. He certainly knows what he's taliing about.

and yes, I agree about the accuracy of Pool Math. Its almost shocking how accurate it is.

I can also vouge for Jason's pool math. It is incredibly accurate!

 

[bdavis466]

PH 7.9-8.0
TA 275
CH 125

Looks like 2 oz of acid per hour is keeping it in the 8.0 range

 

[bdavis466]

Just checked the spa

Ph 7.9
TA 140
CH 125

Where did the alkalinity go?

 

[chem geek]

When the plaster cures and calcium hydroxide is replaced with calcium carbonate AND you add acid to keep the pH down, the TA will drop. This is normal and during the first three weeks you can add baking soda (sodium bicarbonate) to keep the TA higher than normal to keep the saturation index strongly positive. After the third week, you can let the TA drop or if it is not dropping enough (from acid addition used to maintain the pH) then you can add acid and aerate the water.

Basically, the bicarbonate in the water is becoming carbonate in the plaster strengthening it. This is a good thing but means you need to replenish the TA until the 3rd week after which you can let it drop to a normal level.

 

[bdavis466]

Well that's a good thing then. Thanks for the explanation

 

[onBalance]

Looking good now. You got the TA down to the proper range. A pH of 7.8 to 8.0 is just fine. Lowering the pH below that will just consume more TA which will have to be replaced.

 

[bdavis466]

Finished filling at 7:00 this morning. Ended up being 33,000 gallons per the meter at 28 gpm fill rate.

Ph 8.2
TA 375
Ch 125

I have added 1 gallon of acid, 122 pounds of bicarb, and 3 bottles of Jack's magic thus far

The pump is running at 1600 rpm, 1 psi per the filter and 360 watts. I added 10 pounds of DE for the quad 100. Is this pump speed adequate?

 

[bdavis466]

 

[bdavis466]

PH 8.0
TA 350
Ch 125

 

[bdavis466]

Pool has been full for 24 hrs and circulating continuously.

PH 7.9-8
TA 375
CH 125

Looks like I'm going through a gallon of acid per day. Shouldn't the TA be dropping? I haven't added any bicarb since I shut the water off

 

[JasonLion]

I am not completely familiar with what to expect. Still, as the plaster cures it will raise PH, TA and CH. It is plausible that your lowering of PH and TA is canceling out the curing process raising of PH and TA. If I am correct, I would expect CH to go up slowly. You are doing the test by steps of 25, so there might simply not be enough precision to see the behavior of TA and CH levels clearly.

 

[bdavis466]

I was expecting the TA to go down slowly and it almost seems like it may be going up. CH has not changed at all

Doing the TA test in 25's has still used up most of the R009. I already had to reorder

 

[onBalance]

One gallon of acid would only lower the TA by about 15 ppm. Testing accuracy is difficult with that high of TA due to a non-precise color change end-point. (When the TA is high, the actual pH end-point is lower than when the TA is 100 ppm.) You will soon see that the TA will start coming down during the next two weeks.

Also, the high TA is preventing any calcium loss from the plaster surface and increasing the pool water's content of CH. So that is good. That (high TA) also keeps any alkalinity material from being drawn out of the plaster surface too.

Keeping the pH at 7.8 - 8.0 with small amounts of acid as you are doing is good. After about two weeks, start lowering the TA with larger amounts of acid. Use your "Acid-Demand" feature of the your test kit to determine how much can be added at a time.

Once the TA begins to lower, you should begin to add some calcium chloride to increase the calcium (CH) level to 200 ppm over time.

 

[bdavis466]

Are you not expecting the CH to rise on its own even over a few months to a year because of this start up process?

 

[chem geek]

Ideally, the CH should not rise at all because you will have created a water-tight calcium carbonate seal in the plaster surface. Again, the purpose of the bicarbonate startup is to convert the calcium hydroxide produced during curing into calcium carbonate solid that stays as part of the plaster. Now over time there may still be some slower curing or water with bicarbonate migration that converts more hydroxide into carbonate so basically a slower version of what you experienced during startup. In that situation, the pH will rise and acid addition will lower both pH and TA.

However, the pool may also have carbon dioxide outgassing though that should be lessened at a lower TA level. With carbon dioxide outgassing, you would see a similar effect that you add acid and the pH and TA get lowered. Basically, the process of carbon dioxide outgassing has the same apparent result to the water as the plaster curing in a bicarbonate start-up. This is because the net result of the two equations I showed earlier is the following:

2Ca₃•SiO₅ + 3HCO₃^- + 4H₂O --> 3CaO•2SiO₂•4H₂O + 3CaCO₃(s) + 3OH^- + heat
Tricalcium Silicate + Bicarbonate Ion + Water ---> Calcium Silicate Hydrate + Calcium Carbonate + Hydroxide Ion + heat
Soft Uncured Plaster + "TA" + Water ---> Hard Cured Plaster + Hard Limestone + "High pH" + heat

When carbon dioxide leaves the water it effectively remove carbonic acid from the water so looking at this from the point of view of bicarbonate ion it is like the following:

HCO₃^- ---> CO₂(g) + OH^-
Bicarbonate Ion ---> Carbon Dioxide + Hydroxyl Ion

So the two processes are indistinguishable in terms of the water chemistry and the need for adding acid to lower the pH that also results in a lowering of TA. Another way to look at it is that with the bicarbonate startup carbon dioxide is getting incorporated into the plaster as carbonate which is why the net effect on water chemistry is the same as carbon dioxide outgassing:

2Ca₃•SiO₅ + 3CO₂ + 4H₂O --> 3CaO•2SiO₂•4H₂O + 3CaCO₃(s) + heat
Tricalcium Silicate + Carbon Dioxide + Water ---> Calcium Silicate Hydrate + Calcium Carbonate + heat

Now if one does not maintain good water chemistry so that the water is not saturated with calcium carbonate, then two things could happen. One is that any additional curing that produces calcium hydroxide could have that go directly into the water raising the Calcium Hardness (CH) and raising the pH and TA such that acid lowers both (so the net result is a rise in CH) which I designate below as "traditional plaster curing" though it's most extreme with an acid startup. Another thing that could happen is that calcium carbonate could dissolve into the water which raises CH, pH and TA with the main distinction from the calcium hydroxide situation that the pH doesn't rise as much so after acid addition there is a net rise in TA. I summarize these net effects below:

PROCESS .............................. CH .... pH .... TA .... TA (after acid to maintain pH)
Bicarbonate Plaster Curing ......... 0 ...... + ...... 0 ....... - ... one carbon dioxide replaces two hydroxide as carbonate plus water
Carbon Dioxide Outgassing ........ 0 ...... + ...... 0 ....... - ... carbon dioxide leaves the pool
Traditional Plaster Curing .......... + ..... ++ ..... + ...... 0 ... calcium hydroxide dissolves into water
Calcium Carbonate Dissolving .... + ...... + ...... + ...... + ... calcium carbonate dissolves into water

In the ideal bicarbonate plaster curing situation, every 4.7 ppm TA drop after balancing pH with acid corresponds to 10 ppm CH equivalent of calcium carbonate formed in the plaster (but of course you don't see a CH change because the calcium remains in the plaster as solid). You'll know you have the best possible plaster startup when the CH doesn't rise at all and you do not see plaster dust.

 

[bdavis466]

Incredible! The more I understand the process the more glad I am that I went this route. Thank you again for taking the time to educate me.

I suppose I am in good shape then. CH has not changed at all and I see no dust.

Why wait to add the calcium then? I would think that I would want the water at 200 as soon as possible? Is there a reason to keep it on the lower end.... Scaling?

 

[onBalance]

Yes, you have that right. You risk the slight possibility of scaling if calcium chloride is added too soon and while the TA is too high. That why you should wait until the TA is brought down to about 200 ppm and below.

Chem geek has correctly defined and explained the process and the beneficial aspect of the Bicarb start-up.

Since pool water is often not properly saturated (balanced) relative to calcium carbonate during the first year, it is incorrectly and unfortunately assumed that cement hydration (hardening) naturally releases calcium and alkalinity from the plaster surface and thus increases the TA and CH of the pool water.

Be sure to start brushing your pool now.

 

[bdavis466]

So the pool has been full for one week

PH 7.8
TA 350
CH 125

I am planning to keep the levels here for at least another week. The PH rise has already seemed to have slowed down slightly. I have been using tricolor tabs in the skimmer since day 3 but I doubt the chlorine and CYA levels are worth measuring at this time.

I think I will raise the CH to 150 next weekend and in two weeks begin to slowly lower the TA. The water is clear and there is no dust. I am brushing at least twice a day and using the manual vac...so far I'm very pleased

 

[bdavis466]

The pool has been up and running for a little over a month now. My current readings:

FC - 4
PH - 7.2 (to lower TA)
TA - 90
CH - 275
CYA - 40

I haven't kept track but I am pretty sure I've used well over 60 gallons of acid to get to this point. My PH was never allowed to go over 8 or under 7.8 during the initial curing process. I had to check the water and add acid twice daily to maintain this. To lower the TA, I drop the Ph to 7 and aerate to get it back up.

I used a little over 220 pounds of bicarb total. I maintained the TA at 300-350. CH was 125 and never budged. Everyone says the tap water here is very hard but I get 125 every time I've checked it. I hope this isn't the case. I've added 24 pounds of calcium to get to 275. How would I know if my reagent is bad? Would the test read lower than what is actually there?

The pool has been perfectly clear since day one. The only plaster dust that I have seen was when I cleaned the cartridges out on the robot...and that was a minimal amount compared to what I've seen in other pools. The only downside I have seen is a slight amount of scale at the waterline (EDIT...I now know that this is was not scale, my water balance would not have allowed it. It is more than likely effervescence from the man made rock coping). I'm not sure if this was a result of the bicarb start-up or not. I followed the start-up procedure exactly as written so I'm not sure why this occurred? This is what made me think that my calcium level may be higher than what I am seeing when I test.

Now that I am getting everything is balance I noticed that the following numbers leave me with a CSI >-0.6:

FC - 5
PH - 7.5
TA - 60
CH - 275
CYA - 80
Salt - 3500
Borates - 50

CSI= -0.75

By raising the Ph to 7.8 I get -0.59 which is way too close to being corrosive. These numbers are per TFP levels so why are they so close to low end of CSI?

I would like to keep my TA low to help the Ph rise but it looks like this isn't going to work. What are your recommendations? Not using borates seems to help as well but I already have 100 pounds of boric acid thats ready to fall in...