Drained and refilled - adjusting alk and calcium

[dhale1]

Pool was drained and refilled after repair. My numbers are:

25,000 inground gunite pool (white plaster)

CL 1
CC .5
TC 1.5
ALK 20
PH 8
CAL 30
CYA 0
TDS 0

Ok, so I know I need to adjust everything so here's what I did. While refilling, once I got up past the return jets, restarted filter. Shocked with Dichlor (figure that I could add cl and cya at the same time since cya is 0). That was last night. Added some acid last night and put one Trichlor tab each skimmer to keep PH down.

Got home this evening and the cl was back to 1. But, no CC. PH was high again around 8. So I added some acid. About 1 hour later I added about 3 pounds of baking soda.

So, I know I need to add calcium and after searching the forum I realize I should have adjusted the calcium before trying to get the alk up. Question is, how soon can I add the calcium to the pool? I don't want to create a milky mess by trying to adjust both at the same time. Can I get up in the morning, and add the calcium or should I wait until tomorrow evening?

And, can I add a quart of Polyquat 60 now too?

Thanks for any help.

[duraleigh]

I don't think there's any rush to adjust Calcium. It certainly needs to be brought up but I doubt there's an immediate need to get it done.

If you're planning on keeping the pool open for a while, I would suggest keeping the chlorine up into 2-5ppm range and adjusting the pH as the first two priorities. You could put 2 pucks in each skimmer and perhaps get your Cl up, add a little CYA, and control your pH all at the same time.

The pucks will not give you much CYA if you're staying open all winter so you'll need to buy some seperately.

Along that same line, Cal Hypo would chlorinate for you and add calcium but not enough calcium to make much of a difference so you'll have to add that seperately as well. I think I'd try to move the Calcium maybe 50ppm at a time instead of try to get to 200-400ppm all in one dose. I believe you can add it whenever you like over the next couple of weeks or so. Again, I am not aware of any reason to rush it into your pool.......keeping your Cl and pH in line would be my first step.

PS - I think you're gonna need a whole lot more baking soda. Did that three pounds make much difference? Bleachcalc tells me you needed about 35 lbs initially. What are you using to test?

[chem geek]

I respectfully disagree with regard to raising Total Alkalinity (TA) and Calcium Hardness (CH). The current numbers result in a saturation index of a little less than -1.0 and though I know that generally speaking the index is overrated and overrused (or misused) and that one has quite a bit of leeway before there is a problem, I think the water is too aggressive and will leech out or pit the gunite/plaster, at least over time. If you have lowered your pH to 7.5, then you are creating very aggressive water. I don't see any experience on this forum on the corrosive side of the water except for low pH which affected metals, but on the scaling side people usually reported seeing something when the index was > 1.0 (some saw cloudiness at +0.75).

You said that you find that your pH has a tendency to rise (and you are already at 8.0), this could very well be due to your dissolving Calcium Carbonate from your gunite/plaster because that is the effect you would see -- a rise in pH of 0.5 would also raise the TA and CH by about 2 (not measurable). Your TA is quite low so I doubt that you are experiencing any noticeable carbon dioxide outgassing which is the other source of pH rise. If your pool was new or if the repair involved new gunite/plaster, then the pH rise could be due to curing of the new gunite/plaster.

If I were you, I would add both calcium chloride to raise the CH and sodium bicarbonate (baking soda) to raise the TA. Even if you added half of the recommended amounts to get to a TA of 50 and a CH of 150, that would still be a lot better than the situation you are in now. You can then see if your pH has the strong tendency to rise or not (the higher TA will cut down that tendency, but the key is how much acid you need to add over time to maintain pH). If your pH still has a strong tendency to rise, then this is likely the curing of the new plaster/gunite and will take months to subside (you'll just have to stock up on acid).

Richard

[duraleigh]

Hi, Richard,

I'm not sure we're too far apart. My thinking was sanitizer in the pool as a priority and some acid to get the pH in the 7's. Then adjust Alk and Calcium.

It sounds like I may be underestimating the urgency for Calcium and Alk. Are you saying you would address them first?

[chem geek]

Yes, we are in agreement now that I understand your priorities you were describing. I absolutely agree that getting the sanitizer level up (i.e. adding chlorine) is first and foremost in importance. I would also add the TA and CH very shortly thereafter as it is also important, but not quite as time-critical.

I don't believe the pH is as critical since the higher pH actually makes the water less corrosive and "buys time" until the TA and CH are adjusted. The chlorine is most important, but the pH, especially a high pH, is not a problem at all when the TA and CH are so low. Once the TA and CH are added, then the pH can be adjusted. If the pH creeps up too much and/or the water gets cloudy when adding the TA and/or CH, then the pH can be lowered with acid before more TA and CH are added.

Richard

[duraleigh]

but the pH, especially a high pH, is not a problem at all when the TA and CH are so low. Once the TA and CH are added, then the pH can be adjusted. If the pH creeps up too much and/or the water gets cloudy when adding the TA and/or CH, then the pH can be lowered with acid before more TA and CH are added

That makes good sense and helps me understand that relationship a little better. Thanks.

[dhale1]

Thanks for all the replies. My pool was not replastered, just acid washed and a couple small patches. I went ahead and added calcium yesterday morning and a quart of polyquat 60 last night. Anyway, here' s my numbers now.

FC 3
CC 0
TC 3
PH 7.4
CH 130
ALK 80

So, my next question is: Should I get my calcium up to 200? The guy at the pool store said that since I was closing my pool next month that I should leave the calcium where it is until next year. I said I thought that it needed to be between 200 and 400 and he said not for the winter. He told me if I get it up to 200 then there's more chance for scale to form over the winter since the water is not circulating. Any thoughts?

[duraleigh]

I think I would bring the calcium on up to 200. Scaling will occur only if you lose your grip on pH and Alk and you seem to have a good handle on that. I believe the calcium requirement for a gunite pool is year round. Perhaps not as much in cold weather but I see no harm in bringing it up now.