Acid demand with new plaster

[Dodger]

Hi,

Happy to make my first real post and request for advice. Our new Quartzscape Plaster was completed June 8, a few months ago. I believe I've got everything balanced to the TFP SWG ranges. The water looks good (note minor algae comment below.)

I test chlorine and pH every day, TA & CYA about every 10 days, CH about twice/month as everything gets settled. I'll post my latest readings below. My main question is about acid demand. I am going through one gallon of 31.45% MA every 5 days, adding about 1/5 gal each day to maintain pH in the recommended 7.2-7.8 range, though my range is more typically 7.4-7.8. I've read varying opinions that acid demand will be high on new plaster in the first month, or the first 3 months, or the first 6 months, or the first year. So maybe this is normal. But 1 gal/ 5 days of high concentration MA seems a lot more than the posts I've read of other high acid demand + SWG cases.

With this high acid demand, I am also adding Baking Soda once or twice a month to keep TA in range (60-80). I've read some of the info about carbon dioxide outgassing less at lower TA, but I don't see a difference in acid demand whether TA is on the 60 side of the range or the 80 side. Since the outgassing is also worse with lower pH, I'm debating whether to raise my pH target range to 7.6-7.8, but trying to keep that range may be impossible, and I assume it would hit 8.0 a few times per week.

This week I have shut off all the other features (waterfall, in-floor, spillover) that may add aeration to see if that has any significant effect on the pH rise. I'm not sure how much the relatively high surface area (stats in sig) of this pool contributes to CO2 outgassing; I do not have a cover, though I could make use of my homemade lily pads if that would help.

One last thing: I've had a few small outbreaks of mustard algae, but it seems like I meet the exit criteria for the SLAM (FC drop is 0.6ppm overnight, and CC is 0.2). Not sure this issue relates to the acid demand, but I want to fully disclose.

FC = 4.6 (drop to 4.0 in the morning)
CC = 0.2 (was 0.0 last week)
pH = 7.8 (added 1/5 gallon MA after this reading)
TA = 80
CYA = 80
CH = 380
Salt = 3300-3400 (per AquaPure readout; pool stores are getting 2700-2900)
SWG set at 30% for 10 hrs/day

Thanks for your help.

 

[AftonJeeper]

One issue with SWG pools is the constant pH rise. Other forms of aeration as you mentioned do not help the problem. Some people install a pump just to inject acid because of this problem.

You could try reducing your TA to 50 and see if that helps slow the rise. Another thing to check is next time it gets to 7.8 maybe monitor it for a day or two to see if it continues to rise. Some pools are only happy at the top of the range.

You'll want to keep a closer eye on your CSI score if you let the pH drift higher.

 

[Miamipool]

My new plaster, SWG, waterfalls, bubblers caused my pool to do the exact same thing. It seems to get better after six months, I'm now at almost two years and 10k gal pool takes around a gallon a month to keep it in range.

 

[Dodger]

Another thing to check is next time it gets to 7.8 maybe monitor it for a day or two to see if it continues to rise. Some pools are only happy at the top of the range.You'll want to keep a closer eye on your CSI score if you let the pH drift higher.

It looks like it did rise from 7.8 to 8.0 in about a day, but I'd like to pursue this idea that my pool prefers the higher end of the 7.2-7.8 range. It would really help if I had a pH tester with better resolution than the R-0014 color comparator on the high end of the 7s. If I'm going to try hanging out in the 7.6-7.8 range, I will have some excursions to 7.9 or even 8.0. I need more than that 7.8 color to gauge where I'm at. I have a hard time imagining the 0.1 changes up and down from that weird 7.8 shade. The 8.2 is a clear, vivid pink, but what shades happen before that? The other end of the scale, in the bottom half of the 7s, are easier for me to imagine (yellow transitioning to orange).Thanks

 

[AftonJeeper]

I have a hard time imagining the 0.1 changes up and down from that weird 7.8 shade. The 8.2 is a clear, vivid pink, but what shades happen before that?

There are digital pH meters available if you are interested. I have no experience with them but others here have found them useful.

 

[Dodger]

Okay, I've ordered the digital meter, as well as a Taylor 9056 test cylinder (and R-0004), which will give me increments of 0.2 color reference between 7.0 and 8.0 (my current comparator is the one with 7.5 then 7.8 then 8.2).

In the meantime, I wanted to report that my acid demand has reduced by about half in the past 3 days. Yes, I've reduced my pH target to 7.6-7.8. It may drift to 7.9 overnight - is that bad? It's better for my CSI, but I'm not sure about other factors. I'm also wondering how much our weather change the past several days has affected pH. The CO2 out-of-equilibrium chart shows pH versus TA at 80 degrees F (I assume this is water temp). Do we know how those numbers are affected by drops in temp? Last week, my water ranged naturally from 72-78 F. Now the range is 65-70 degrees F.