I've lowered my TA to 40 to try to stabilize pH (which still climbs, but more slowly). Here are my current numbers:

FC- 5
pH- 7.8
TA- 40
CH- 420
CYA- 35
Salt- 2000
Borate- 50
Temp- 62

According to the Pool Calculator, CSI is -.54; if I lower pH to 7.5, CSI rises to -.71, which could affect our gunite surface. I'm thinking I should raise CH to 550-600. Should I raise it higher? Would there be any problems with that? Is there any upper limit of how high I could go?

Thanks!

I would leave the pH at 7.8 and raise the TA to 60 ppm.

You could raise the calcium a little, but I would rather try to keep it lower to avoid excessive levels that are hard to lower, if necessary. I would say that the upper practical limit for calcium would be somewhere around 2,000 ppm before it started to become really unmanageable. Your specs don't show a salt system, but since you're giving a salt level, I'm guessing that you might have one?

Thanks, James. I don't have a SWG- just have salt for the feel.

If the upper practical limit is somewhere around 2000, why would you prefer to raise TA? When TA is at 60, I'm adding MA every 2 weeks to keep the pH from going over 8.0.

Is your pH truly consistently more stable when the TA is at 40 ppm? The pH can rise from other sources such as curing of plaster. If you really know that a TA of 40 ppm is very helpful to you, then yes you could raise your CH even up to 1000 ppm. Just note that you don't have much leeway and if your TA rises, say from evaporation and refill, that your saturation index will rise as well (especially if the pH rises). Of course, we're not talking about huge swings and you will be in a reasonable range regardless. The main point James is making is that while it is easy to raise CH, it's hard to lower it so you really have to be sure that your TA and pH are in a stable place if you plan on raising your CH because going back is hard (i.e. requires significant water dilution).

Normally we only find that a low TA level of 40 or so is required for spas due to the extra aeration from ozonators and spa jets in a small volume of water. In pools, it's more unusual unless there are significant waterfalls, spillovers, vanishing edges or other sources of aeration. Do you have a lot of aeration in your pool?

I think that 40 ppm is a little low for TA. I am always cautious about going too high on the calcium. 2,000 ppm is kind of an upper maximum manageable level, but it best to try to stay well away from that whenever possible.

I think that you could raise it a bit with no problem. I would leave the pH at 7.8, raise the TA to 60 ppm and raise the calcium to 500 ppm. I would do the calcium first, and do the TA the next day.

My personal preference is to not be too concerned about the pH, even if it gets to 8.0, but that is not something I would recommend because it can end up causing problems if you're not careful. I think that the pH is OK as long as it's definitely not over 7.9.

Also, a higher pH can lead to metal staining if you have metals, so you have to take that into consideration. If you have copper or iron in the water, then keeping the pH higher can be a problem.

When balancing for CSI, you have to calculate what the CSI will be at the maximum and minimum water temperature and make sure that none of the parameters are too far off at those temperatures. The problem with calcium is that it is not easy to lower if necessary. If you don't have problems with calcium buildup, then raising the calcium somewhat should not be a problem. You could go to 600 ppm on the calcium if you want, but CSI is still going to be a bit low.

You're kind of at a point where it is somewhat of a personal choice exactly where to keep the CSI and the individual levels.

Also, note that the borates and cyanuric acid make up part of your TA. Therefore, your carbonate alkalinity is lower than 40 ppm for purposes of determining CSI and pH rise.

At a pH of 7.8, the 50 ppm of borates will account for 10.11 ppm of the TA and 35 ppm of cyanuric acid will account for 12.11 ppm of the TA.

Therefore, the Carbonate Alkalinity is only 17.78 ppm. That does not give you enough margin for error, and is why your CSI is so low.

Your carbon dioxide level is about 0.550 ppm, which is very close to the equilibrium point with the ambient air.

Play with the other parameters before you mess with Calcium. It will grow all by itself with California hard water. When mine hit 1100, it got increasingly difficult to keep CSI safe. Each time I add about 2" of water, my CH goes up 25 ppm, so it can grow fast. And when the water warms up into the 80s, you'll still have that Calcium in there.

So what I am hearing is that I don't want to go too high with the CH, because if I ever get to a point where I have to lower it, it would take quite a bit of drain/refill to get it back down. In playing with the Pool Calculator, if I raise CH to 600, then even if pH goes up to 8.0, TA to 80 and pool temp to 90 (all upper limits for me), then CSI is ~.53. At CH of 700 it would be ~.59. So I am thinking of raising CH to 600-700.

Any flaws in my thinking?

Thanks everyone for your input!

While some southern California water is hard, not all water in California is hard. For the San Juan Water district, the hardness is 29 with Calcium at 8.8. For the Sacramento Suburban Water District (SSWD), the hardness is 112 with Calcium at 23 for the NSA groundwater supply. I don't think CH buildup from evaporation/refill is going to be a significant problem in your area. Check your specific water district report or better yet test the CH of your tap water yourself to be sure. Where I live, the Marin Municipal Water District has a weighted average (from two sources of water) hardness of 75 ppm while the measured CH of my tap water is 55 ppm.

I've been kinda chasing the same rabbit. Trying to get my TA low enough to avoid having to add MA often. I was concerned about the CSI level. I eventually raised my CH to 525. My numbers work out pretty well. I do have a SWCG so I get some aeration there hence the PH rise and the need to add MA. I test regularly and maintain the PH between 7.5-7.8. I am also using borates. Your logic sounds reasonable for raising your CH level.

chem geek and bobodaclown- you guys make me feel bedda!

One last question- I've heard you can do a CH test using 10 ml of pool water rather than 25 ml. Would I still use 20 drops of R-0010 and 5 drops of R-0011? (Then multiply by 25 rather than 10, of course.)

As noted in the Taylor K-2006 Instructions, for the CH test:


So they have you use fewer drops of the initial reagents, though not quite proportional. The amount needed for the calcium buffer and indicator dye are not critical -- they just need to be in the ballpark to buffer the pH and to have enough dye to see a decent transition.

Thanks!

You should keep the CSI within +/- 0.3.

+0.53 would be too high. I wouldn't raise the calcium over 500 ppm. I would raise the TA to 60 and allow the pH to go to 7.9.