Curing new plaster?

[JJParrish]

After having our pool re-plastered in March, the pool guy came out w/ FOUR gals of Muratic Acid. He said he had been told to put in 8 gals, but only had 4 gals on his truck..... Well, we never got the big dust clouds when brushing daily, just small amounts. After the initial 4 gals, we kept adding the acid to keep the ph knocked down, as per instructions. The question is, would the initial start-up w/ 4 gals do any damage to the new plaster??? Or, what are the pros and cons of having a start-up like this? Love this site, Joyce

[JJParrish]

....any and all comments are welcome and appreciated. Thank you. Joyce

[mas985]

Sounds as though he may of did a partial acid start but the objective was the same to minimize the calcium dust. So it sounds as though it was successful.

An acid start is different than a standard chlorine start and bit more complicated. However, to do it properly, you should follow a set of steps which at the end includes raising the PH. So here is what I understand to be a proper acid start.

1) Add enough acid to drive total alkalinity down to 0. 8 Gallons sounds about right for 18,000 gallons but 4 was probably a bit less than needed. PH will drop considerably during this phase. This should be done within a 24 hour period if possible which is why a bunch of acid is added at once.
2) Most if not all of the calcium dust will dissolve during the next couple of days and the surface may soften a bit but should not dissolve so you want to avoid brushing at this step although at light brushing should be ok as well.
3) After 3-4 days, the PH should be up by now but if it isn't add enough borax to bring up to at least 6.8 and start the circulation pumps. Add chlorine as needed. Now you can start brushing.
4) After a week, maintain as normal. Some of the calcium may drop out of solution so you may need to backwash quite a bit over the next few weeks.

Acid starts are generally not a bad way to go but you need to make sure that the PH and alkalinity do not stay low for more than 5 days otherwise the surface may start to dissolve.

[JJParrish]

Thanks for the info, Mark. What does it mean, or what does it look like, or how would we know if/when "calcium may drop out of solution"? BTW, the pool was replastered in MARCH and our water has been kept balanced since about a week or so after the initial acid (ish) start. Also, is it possible for "calcium to drop out of solution" at any time, like now? Thanks, Joyce.

[mas985]

Normally, the calcium stays dissolved in water and the calcium hardness just goes up. But sometimes, if your TA, PH and calcium are on the high end, calcium can start to collect on the floor and/or walls of the pool as scale. If you have not seen it by now, it probably won't be a problem but post your numbers and someone will chime in if anything is off.

[JJParrish]

Thanks Mark. I will get the pool store to check my water tomorrow and then I will come home and use Ben's kit. It will be late afternoon before I can get this done. Thanks again. Joyce

[JJParrish]

Thanks for all the help. Got some numbers:

[JJParrish]

Oops, I hit the wrong button and the edit knocked me off! .......Thanks again Mark. Sorry so late getting back. Big day. Got the numbers:

Ben's Kit Pool Store
FC 3.5 FC 2.9
CC zero CC -1.9 (minus 1.9?..they say)
TC 3.5 TC 1.1 (do not understand their chlorine stuff)
pH 7.6 or 7.7 pH 7.5
Alk 110 Alk 80
Cal 230 or 240 Cal 196
Cya 20-ish Cya 26
Temp 82 Temp 85

BTW, keeping the FC between 3 & 6 per this site. I add 3 quarts per night and it seems to hold okay. I am planning to up my Cya to about 30 or so and see how it does there.

Some other numbers from pool store are: Saturation Index, -0.09, Total Dissolved Solids 500, Iron 0, Copper 0. I took the water straight to the pool store at about 11 AM and could not get back home to test w/Ben's kit 'til 6:30 PM....just in case the time lapse makes a diff. I feel like the water is doing good, but I kinda expected the white plaster to be like really white, like the 'white' it looked like when the guys were plastering and the sun was shining on it! It does look a little tad dirty, grayish, sorta, but it is only noticible when you are down there looking right at it! Thanks for your help. Joyce

[JJParrish]

...sorry about the numbers running together, they were not like that on my reply. Ben's kit is left and pool store is right.

[chem geek]

The numbers look very much in balance as far as calcium carbonate saturation goes. So I doubt that there is precipitation of calcium carbonate occurring. If the plaster were curing, then you would find that the pH and TA would rise a lot (mostly the pH) and that eventually you would measure a rise in CH. That is what happens with curing. So if you let your pH get to, say 8.0 or higher, then you might see some calcium carbonate forming, but I don't think that is happening.

Basically, your water is in decent water balance now, but if the plaster is still curing you will find a strong tendency for pH to rise and you'll be adding lots of acid to keep the pH down to normal levels (around 7.5) and doing so will restore the TA to where it was.

Richard