pH advice for a traveling man's pool

[Verne Bunsen]

Hello all,

I'm looking for some advice on how best to handle the pH in my pool. The pool chemistry is really quite stable, but the catch is that I travel for work and am routinely gone for two weeks at a time. I have been in the habit of lowering the pH with MA to close to 7.0 before I leave, giving it room to drift up while I'm away. It used to drift off the scale, but since recently adding borates it seems to drift quite a bit less, up to 7.7 the last go round. It has been a workable system and the pool water and equipment are faring well, but I've recently been spending some time with the Pool Calculator (nice work on that, by the way!!) and running hypotheticals on the calculator tells me that taking my pH below about 7.4 brings me in to trouble territory on my CSI. My pool surface is Pebble Tec, which I think is similar in nature to the plaster/masonry surfaces as far as chemistry is concerned?

TF-100 water tests from yesterday:
FC 7.0 ppm
CC 0.5 ppm
pH 7.5
TA 70
CYA 70
CH 530
Salt 3200 ppm
Borates 50 ppm
CSI -0.31

With all other parameters the same, reducing pH to 7.0 drops CSI to -0.72.

The high CH is kind of a mystery to me, my fill water is CH 180. I do have evidence of some scaling at my spa overflow and at the water line.

So I'm trying to avoid high pH to prevent excessive scaling, but now I'm learning that low pH (neutral) has risks as well. My situation doesn't allow for managing it right in the 7.4-7.8 window, so what's my best course of action?

Pool history in case any of it is relevant:
I've owned this house for right at one year. I moved to Arizona from Alaska, so had very little pool maintenance experience. I hired a local pool company to maintain it and had them start by draining, acid washing and bead blasting, and refilling the pool. So the water in the pool is just about 1 year old. At this time, the SWG was non-functional and the pool was chlorinated by a floating dispenser. I don't know exactly what product they were using. They typically made their rounds while I was out of town, and my wife reported that they were usually only there for a couple of minutes, basically just long enough to drop off the invoice. I happened to come home on the day of one of their visits, and found skimmer and pump strainer (which they were supposed to be taking care of) full of debris. I also found the chlorine float empty. I took a sample to Leslie's and they found zero chlorine in the water. I fired them immediately. With the help of the folks at Leslie's, I got my SWG back in service and got the salt levels up where they needed to be. At that point I ordered the TF-100 and started doing my own testing and maintenance. My CH was 490 at that time (this was just 5 months after filling the pool with new water) and has bounced around between 490-630 ever since.

Sorry for the super long post, but more info is better, yes? Thanks in advance for any input!

 

[anonapersona]

Could be the pool service was shocking with a lot of cal-hypo, but that would be a LOT of cal-hypo. Just following that thought, that could be why the SWG was not in operation, excessive scaling. So your acid wash and bead blasting would have cleared the visible surfaces but perhaps the piping also has a lot of calcium scaling....just guessing here. Was there any leftovers of the product used in the floater, normally that would be 3" pucks of trichlor, but there are also smaller things that can be put in skimmers, I think, that are cal-hypo. And cal-hypo is more normally used as a powder form, frequently in pre-measured bags, though a service would use it by the scoop as loose powder.

We will want to let some one who is better at chemistry get in on this, not my field at all, but I will suggest that when the pH is dropped you may be breaking out some of the scaling that I'm guessing is in the pipes. That would say that you will have to keep doing what you have been doing, lowering pH from time to time, and then also do some water changes to remove the CH that appears in the pool.

So, your question... I dunno. I think that low CSI is attacking scaling in the pipes. Now whether it harms the pool, that is probably a question of timing. How long does it take for that low pH to bounce back when you do it? I suggest you conduct an experiment, drop the pH to about 7.0 and test to see how fast it climbes. Your TA is not enough to drive it up rapidly, IMO, so if it rises in a day or so. then maybe pipe scale is consuming it.

But, let's see what the chemistry smart folks here have to say...

 

[JasonLion]

CH does not evaporate. With fill water CH at 180, every time you top off the pool you are adding more CH, so the level goes up. This is a common problem in your part of the country.

To slow down the PH drift you should not lower PH as far as you have been doing and also lower your TA level down to 50 or 60. PH goes up more quickly when the PH is low and when the TA is high. Changing both should have a fairly significant effect.

 

[Verne Bunsen]

Thanks for the input, guys!

Anonapersona, I hadn't considered the possibility of scale in the system contributing to rapid pH rise, I will investigate that further. From what I have seen of the piping internals when removing the SWG cell or opening up the filter, there's not much sign of build up, but that doesn't necessarily mean anything.

Jason, that makes sense regarding the CH. The water evaporates out and the concentration steadily increases. The TA was at 90 when I took over the maintenance. It migrated down steadily with my MA treatments for pH and has leveled off at 70 for the past couple of months. Will making smaller but more frequent MA treatments be likely to get the TA trending down again?

 

[JasonLion]

Any acid additions will lower the TA. Lowering TA tends to take a while, especially when TA is fairly low to begin with.

 

[Verne Bunsen]

Got it, I'll keep at it!