Fighting Scale and High pH in pebbletec SWCG pool

[steeeamy_nicks]

I have done a great deal of searching and reading, and I'm really left with just a few questions here, let me describe the situation:

20k gal
pebbletec finish
SWCG
Jandy LXi heater

FC 3
CYA 70
TA 70
CH 250
Salt 3200

The pH will rise from whatever I bring it down to with muriatic (usually 7.3-7.3) up to prob 8.5 or so within a few days.

The temp stays in the mid 80s during the summer, and gets down as low as 50s over the winter.

I have two bubblers on a tanning shelf and a spillover from my spa, so as you can imagine I fight pH rise from aeration a good bit, and I play the vicious cycle game with adding bicarb to keep the TA up, as recommended by my equipment manuals.

I have seen people on this forum discuss keeping alkalinity lower to fight pH rise due to co2 offgassing, but unless I kick the CH up a good bit, that's going to leave me with aggressive water, no? Won't that eat out my heat exchanger?

If I were to raise the CH (possibly shooting for the TA*CH=25000 rule?) wouldn't I just be increasing my scaling issues?

I get plenty of scale on the stones under the spillway, and from what I can tell, this scale is from evaporation and consists of more than just calcium. Which explains why a reasonable amount of muriatic acid and elbow grease are NOT an easy nor effective way of removing this ugly buildup.

Any ideas? Is it safe to run low TA with my equip? If I raise CH to compensate, won't I increase my scaling issue? Anyone have a good way of getting rid of that scale that I couldn't find with a search?

By the way, thanks to all of you, this site is excellent. I've been around pools for a long time and I've learned a lot from reading on TFP since I found it a month ago.

 

[Bama Rambler]

With an swg you're better off letting the TA stay about 70. Given the numbers you posted I suspect that the buildup you're seeing isn't calcium scaling but effervescence or salt. Does it fizz when you use MA (muriatic acid) on it?

You didn't post what the pH runs but that has a big effect on the CSI. You could leave the TA at 70 and bump the CH up to 300.

 

[steeeamy_nicks]

Sorry, if I don't do anything to it, the pH will get up over 8 a few days after bringing it to 7.4 w muritatic. I've even tried going to 7.0. It seems to hit a ceiling at what I'm estimating to be 8.5, as it is good and purple, clearly above 8.0 on my Taylor kit. I'm assuming that is the point at which the excess co2 has more or less run out from off gassing.

The buildup turns the acid yellow and fizzes.

 

[duraleigh]

Regardless of how much acid it takes (it won't hurt anything), it is a necessity to keep your pH in the 7's at ALL times. If you do not, you will continue to be plagued by scaling.

Controlling TA and CH are adjuncts to your pH staying in the 7's.

 

[steeeamy_nicks]

Dave, I do realize that, thanks, however what I'm trying to find out here is if there is anything I can do with the other chemical parameters to minimize the need to constantly add acid. If I can avoid buying an acid or co2 feeding system I'd like to do that as well...

 

[chem geek]

Keeping the TA low and targeting a higher pH (i.e. don't try and lower the pH below 7.5 and instead target 7.7) helps reduce the pH rise from carbon dioxide outgassing. Is your pipe length from your SWG to your first pool inlet short? It may be that chlorine gas is outgassing and not fully dissolving in the pool water (do you smell any chlorine near that inlet when the SWG is on?). You might try pointing the closest return to your SWG downwards to see if that has the chlorine gas dissolve more into the pool water. The addition of 50 ppm Borates can help somewhat, though mostly in slowing down the rate of pH rise and not in the amount of acid you need to add when you do add it.

 

[steeeamy_nicks]

So what are your thoughts on letting the alkalinity drop down below 70? Should I jack up the calcium?

I'd say the run of pipe is about 40ft from the pad to the nearest return, I'll take a closer look at that. Thanks

 

[ping]

Are the bubblers and spa spillover constantly running? If so, that would be the first thing I would resolve. I only run enough water to my spa so that the water trickles down the spillover. Turn off the bubblers if you can and see how fast the pH is rising after you take care of the aeration.

How old is the pebbletec?

 

[steeeamy_nicks]

I run the spillover for a half hour in the AM and an hour in the evening. I will kill the bubblers and see what happens. The pool is a little over 3 years old.

What I'm really wondering is if there is any downside related specifically to having the TA low even if I keep the CSI in check with CH.

 

[dmanb2b]

What I'm really wondering is if there is any downside related specifically to having the TA low even if I keep the CSI in check with CH.

As long as you keep CSI in check, none. Do not drop TA below 50 and anything below TA of 60 I would suggest also using borates to stabilize things out.