New pool results

[ehorn]

I just wanted to get some advice on my results for the pool. It's a new gunite pool about 18k gallons. I've had the pool in service now for three weeks. It's too cold to swim in of course, the temperature of the water is about 50 degrees. I have a Pentair test kit provided by the builder. The results I'm getting so far are:

FC: 3+ ppm
TA: 180ppm
PH: 8.2

From the test kit I'm at the max for free clorine it only goes to 3 ppm. Being it's so cold this is no big deal as there isn't anything in the water to kill. What I'm more concerned is the PH and TA. They seem to be a bit high and according to the kit it would take 1 gallon of acid to lower the TA 30ppm. My target TA is 120ppm.

Any suggestions? Should I just keep adding acid till it's lower?

Eric

[chem geek]

Congratulations on your new pool!

Before taking any advice I give below, make sure you do what your pool builder says since this was a newly built pool. There may be some requirements for you to not violate the warranty of the build. Perhaps they want you to keep the pH or TA high during the curing process of the plaster/gunite (though my guess is that they don't).

The amount of acid it would take to lower the TA isn't something you can get from a kit. The kit will only tell you how much acid it will take to lower the pH (because the lowering of TA involves the outgassing of carbon dioxide and there is no way to accurately predict that since it is a function of aeration in addition to pH and TA level). To lower the TA, you need to follow Ben's Lowering Your Alkalinity procedure which involves adding acid to lower the pH significantly (to around 7.0 or so), then aerating the water while adding acid to keep the pH low, then when the desired TA is reached, stop adding acid and keep aerating until the pH rises to the desired level. Again, check with your pool builder since they may not want you making the water that neutral so soon after a new plastering. If they don't, then you can just add acid to get the pH moderately down to their recommended level, but you'll be adding acid frequently and the pH will keep wanting to rise (Ben's procedure uses the same amount of total acid, so it's a lot of acid, but accelerates the process so you lower the TA much more quickly).

Until you get your TA down, it will be difficult for you to maintain a normal pH. The fact that it is a new gunite pool means that the plaster/gunite is still curing and that will cause the pH to rise significantly anyway so you can expect to be adding acid regularly for a while even after you get your TA lowered. However, right now having the TA so high just makes it that much more difficult to get the pH down and has you using that much more acid so I suggest following the procedure above.

By the way, if your Pentair test kit doesn't also test for Calcium Hardness (CH) or for Cyanuric Acid (CYA), then you should get a better test kit such as the Taylor K-2006 which has those additional tests (and also has an accurate drop-based FAS-DPD chlorine test and of course a Total Alkalinity test). It would be interesting to see what your Calcium Hardness level is since the high TA and pH are almost to the point of causing scaling, but perhaps with the new pool build they have the calcium on the low side since calcium hydroxide is expected to be introduced into the pool through the curing of the plaster/gunite.

Why is your target TA 120 ppm? Usually that high a TA is only needed if you plan on using an acidic source of chlorine, such as Trichlor tablets. Otherwise, if you plan on using chlorinating liquid or bleach, a TA of 80 to 100 ppm is usually more appropriate (80 ppm is better if you have aeration features or otherwise find that your pH tends to rise).

Richard

[CarlD]

I think I can answer part of this:
Usually, Ben's recommendation for Total Alkalinity is 80- 125 especially for gunite/plaster pools. Generally, as you know, pH is easier to keep constant when the T/A is at the higher end.

Other than that, I would agree with Chem_Geek's advice to do what the builder says chemically to avoid giving him an excuse to void the warranty.

The Taylor 2006 or 2006c kit is an excellent choice. Equally good is the Leslie's FAS-DPD Chlorine Test service kit, but Leslie's stores rarely sell it. It's available on-line.

The best kit of all is Ben's test kit available at his sister site to this one, PoolSolutions.com. It's ONE BIG problem is that Ben (PoolDoc) hasn't been selling it for awhile, and, until he announces that he's selling and shipping again, it's just not available.

Still, any of these kits will quickly pay for themselves and you will wonder how you ever got along without them!

[ehorn]

Thanks for the advice. I added one gallon of acid to the pool and it changed the results to:

PH: 7.2
TA: 150ppm

I can run the waterfall and spa with spillover to probably lower the TA to a lower value. The only issue I have right now is our waterfall leaks and still waiting on them to fix it. I'm just glad I got the TA down some from before.

I'm also going to pick up a better test kit, any suggestions as to who sells it for a good price online?

Eric

[chem geek]

Eric,

Though you have reduced the measured Total Alkalinity by adding acid, you actually haven't removed hardly any of the carbonate from your pool. My calculations show that simply adding acid to lower the pH from 8.2 to 7.2 will lower the TA from 180 to 157 just by changing the proportion of different chemical species in the water (you shifted to having more carbonic acid, H2CO3, in the water and that species does not count towards TA). If you were to raise the pH even by adding caustic soda / lye (which does not have carbonate), you would raise the TA back up again. pH and TA move up and down together.

This is why adding acid alone does not really lower the TA in an absolute sense. Only the aeration will do that and aerating while at a lower pH gets rid of the carbonate in the water faster. So when you get your waterfall fixed, start aerating while keeping the pH low and that will truly lower the amount of carbonate in your pool.

Richard

[CarlD]

What Richard says is exactly correct. Since you have a gunite pool, T/A levels are more critical than it would be for a vinyl pool (for vinyl your current t/a would be fine).

You need to aerate your water to raise pH without raising T/A. It's a racheting process--lower pH to 7.0-7.2 (with gunite it can be lower, but you have NEW gunite so stay in the range). This pulls the T/A down. Then aerate to raise pH without T/A rising. Repeat until T/A is where you want it, then aerate to raise pH one last time to normal.

Do NOT confuse caustic soda with washing soda. The first is lye, sodium hydroxide, the latter is sodium carbonate, and is the same as soda ash the pool stores sell (actually, it's not the same--it's FAR cheaper!)

And don't confuse either with baking soda, sodium BIcarbonate, which is used to raise T/A, should you need to do so.