New plaster - Pool Calculator extremes

[novca]

Hello,

We just got our 16,000 gallon pool replastered with medium gray. They wanted an acid startup. 5.5 gallons of acid have been in for about 72 hours. Most of the dust is gone, but there is still some kicked up when brushing 2-3 times per day.

The pH and TA are currently off-scale low when testing with my Taylor test kit, as expected.

When the dust is gone and it's time to neutralize the acid, I can't figure out how much washing soda to use. The pool calculator says that adding 320oz (20lb) of washing soda will raise pH by 4.34 and TA by 141. Obviously I don't want the TA to go up that much, but that may not be enough of a pH rise to get into the 7s so I can turn on the equipment. Do the formulas in the calculator break down at such extremes, or are these numbers accurate?

Is there a better way to tell how much soda ash to use in this situation? The equipment is not on yet, so adding a little at a time and mixing by hand doesn't seem too practical.

As an aside, I have the heater disconnected from the plumbing right now. It's only pump and filter in the circuit. In this case, is it okay to run the equipment prior to the pH getting into the 7s without damaging anything?

Thanks.

 

[JasonLion]

When doing an acid startup with fresh plaster you don't normally neutralize the acid, the plaster curing takes care of that automatically. The PH should come back into range on it's own within one to three days.

The pump and filter should be fine with low PH. It is normally only heaters that have problems (and really only heaters with copper heat exchangers, which are common).

Yes, you normally want the pump running 24/7 for at least a week (and often several weeks) after fresh plaster is applied and the pool is filled with water.

 

[novca]

When doing an acid startup with fresh plaster you don't normally neutralize the acid, the plaster curing takes care of that automatically. The PH should come back into range on it's own within one to three days.

Hmm. I just assumed I needed to neutralize it based on the below-information found elsewhere on this site. I'm also 3 days into it and the pH is still off-scale low. The TA is about 20.

This is a very common start-up procedure, especially for exposed aggregate finishes. Your builder usually does this whole procedure.

Leave the pump off at first.
Add 3 1/2 gallons muriatic acid per 10,000 gallons and then brush the entire pool. The acid will help dissolve the plaster dust so you don't need to vacuum.
Brush twice daily but don't vacuum or add chlorine until plaster dust is gone. For dark plaster only brush lighter colored or white areas.
When all plaster dust is gone, neutralize the acid with soda ash/washing soda by using a base demand test, wait 24 hours and repeat if needed.
When the PH reaches 7.2 or higher, check all equipment and turn on the circulation system. Clean the filter when the pressure increases 10 psi. Add sanitizer in small amounts at first until the desired level is obtained.

The plaster company's instructions were vague at best. They also said to get the CH up to 220 (fill water out of the tap was 175) during the curing process too -- which seems at odds with info elsewhere on this board that says curing plaster increases CH by itself. The independent pool store people said the first step after the dust is gone is to get the TA up before adjusting pH -- which doesn't make any sense to me at all. That seems backwards.

Much of the information about new plaster startup seems conflicting, especially when you're comparing the "I've been in the pool business for 35 years and this is how we do it" guy with the chemist. When it's all said and done, though, I'm more inclined to trust the chemist. This site has served me well for 5 years so far, but there is some conflicting information here as well.

Thanks!

 

[JasonLion]

There are many theories about fresh plaster startups. Many of the details don't actually matter, but our understanding of the science is not complete so it is difficult to tell which of them do matter, making everything confusing.

Generally, the PH will come up on it's own right around the same time the plaster dust goes away, and a day either way doesn't matter much. However if the PH does not come up fairly quickly after the dust is gone you should raise it. Since the curing plaster will have been raising the PH (even if not all the way) there is no way of telling exactly how much soda ash you will need in that situation, presumably not all that much. Generally you add enough to raise the PH by 0.4 or 0.5, wait half an hour or more for it to mix in, test the PH again, and repeat as needed until the PH comes up. But again, chances are the PH will come up on it's own.

Likewise, CH normally comes up on it's own, at least most of the way. But often enough you need to raise it a little. The risk is that since CH will continue increasing, adding too much now could cause problems later. But too little CH can cause pitting of the plaster surface. I wouldn't worry about it at all until it has been two weeks since the plaster was applied, and then raise it to the minimum (250), then wait till it has been a month and raise it more if needed. Given you have high CH fill water, perhaps you shouldn't raise CH, it will tend to go up on it's own as soon as you top off evaporation.

PH and TA are tied together to a fair extent when the PH/TA are both low. Raising one tends to raise the other. This effect is mostly gone at normal levels, though not quite completely. Odds are if you get one of them to the minimum end of the range the other one will be close to acceptable (but usually not quite). After that you can adjust them separately and the linkage between them will be minimal (though not gone). I used to be a fix TA first person, now I am a fix PH first person, but to a fair degree it doesn't make any difference.

 

[novca]

There are many theories about fresh plaster startups. Many of the details don't actually matter, but our understanding of the science is not complete so it is difficult to tell which of them do matter, making everything confusing.

Generally, the PH will come up on it's own right around the same time the plaster dust goes away, and a day either way doesn't matter much. However if the PH does not come up fairly quickly after the dust is gone you should raise it. Since the curing plaster will have been raising the PH (even if not all the way) there is no way of telling exactly how much soda ash you will need in that situation, presumably not all that much. Generally you add enough to raise the PH by 0.4 or 0.5, wait half an hour or more for it to mix in, test the PH again, and repeat as needed until the PH comes up. But again, chances are the PH will come up on it's own.

Likewise, CH normally comes up on it's own, at least most of the way. But often enough you need to raise it a little. The risk is that since CH will continue increasing, adding too much now could cause problems later. But too little CH can cause pitting of the plaster surface. I wouldn't worry about it at all until it has been two weeks since the plaster was applied, and then raise it to the minimum (250), then wait till it has been a month and raise it more if needed. Given you have high CH fill water, perhaps you shouldn't raise CH, it will tend to go up on it's own as soon as you top off evaporation.

PH and TA are tied together to a fair extent when the PH/TA are both low. Raising one tends to raise the other. This effect is mostly gone at normal levels, though not quite completely. Odds are if you get one of them to the minimum end of the range the other one will be close to acceptable (but usually not quite). After that you can adjust them separately and the linkage between them will be minimal (though not gone). I used to be a fix TA first person, now I am a fix PH first person, but to a fair degree it doesn't make any difference.

Thanks.. So today is the 5th day with the new plaster. 90% of the dust was gone by the 3rd day. I still get small amounts when brushing, but not much. The water is basically clear and has been pretty much has been the whole time except the 1st day when brushing.

At the end of the 3rd day I added some trichlor pucks in a floater to start gently introducing some chlorine and CYA.

Yesterday (the 4th day) the TA had come up to 70 (from near 0) by itself, but the pH was still off-scale low (< 6.8). CH is 220. I fired up the equipment and started gradually adding some soda ash throughout the day and again this morning. I've added about 8lb of soda ash in total.

So now I'm at a TA of 100 and a pH of something slightly less than 6.8. I don't want to add more soda ash because I don't want the TA to go any higher. What's the next step? Let the pH come up on its own over the course of the next few weeks as the plaster cures (the trichlor won't be helping this)? Add some borax (but that will still increase TA somewhat)? Other suggestions?

Thanks again.

 

[JasonLion]

Aeration of some kind is probably the best solution. If you don't have a fountain or waterfall, try pointing a return up towards the surface so it creates some turbulence at the surface. The aeration should raise the PH, though possibly slowly.