Now That I Got My Numbers, I Got Questions

[hrustar]

So, here's my water story according to the Taylor k2006:

FC: 0.5

CC: 0.2

PH: 7.8

TA: 90

CH: 275

CYA: Off the charts. Well, well past 100

Saturation Index: 0.5 (not sure what this is, but it seems okay).

No, my questions.

FC is low but CC is high. How can I increase FC while also lowering CC?

Connected to this, since CYA is off the charts and can;t change water due to weather, should I be using bleach rather than dichlor or is there a better option?

My PH and TA are both just a tad high, but I can reduce them without issue using my decreaser product.

CH is a bit high, but seems to be well in the acceptable range. Do you concur?

What is saturation? SHould this concern me?

THANKS FOR HELPING ... Now that I have "good" data, I really want to dial things in.

[chem geek]

A Combined Chlorine (CC) reading of 0.2 ppm is not high -- it is quite low. Anything 0.5 ppm or below is fine for a spa. 0.2 ppm is the lowest reading on your test kit (using a 25 ml sample size) so it's actually <= 0.2 ppm so is quite good.

To raise the Free Chlorine (FC) level, just add chlorine. Since your CYA is off the charts, you could use bleach instead of Dichlor. However, to avoid a rise in pH, you should lower the Total Alkalinity (TA) first to around 70 ppm and then consider using 50 ppm Borates. Either that or consider a drain/refill (of course, it's probably too cold to do that now). The high CYA makes the chlorine less effective so you may have more trouble keeping your water clear. You might need to supplement with non-chlorine shock (MPS), perhaps weekly.

With your higher CH, you'll want to have the TA be a little lower and the pH closer to 7.5 (you lower the pH using acid). The saturation index is actually high and this is mostly due to the high CH. Does your fill water have high CH? A high saturation index can lead to scaling of calcium carbonate, especially in the heater since higher temperature makes the index even higher.

[mcw53]

My 1st recommendation would be to dump and start fresh. But if not an option, definitely switch to bleach. With your CYA so high, you probably need to run higher FC levels because your chlorine will be less effective. At this point I wouldn't worry about CC (0.2 ppm is not really that high). Your nose will tell you if your CC is getting too high. Your high saturation index (CSI) is due to high pH, TA and CH and is definitely a problem that could lead to scaling. You want your CSI to be in the -0.1 to -0.3 range if you've got an acrylic or fiberglass spa. There is nothing you can do about the high CH except replace water. Therefore you need to be running lower pH and TA. I would lower your TA to a level that will support a 7.5 to 7.6 pH. Adding 50 ppm Borates (e.g using Boric Acid) will drop your CSI about 0.1 points.

EDIT: Sorry for the duplicate info; looks like I was composing my reply after chem geek posted his. At least it is not conflicting information.

[quantumchromodynamics]

If we assume a cyanuric acid level of 120, the CSI is only about 0.28, not too extreme.

Subtracting 1/3 of the cyanuric acid level (.33 x 120 = 40. 90 - 40 = 50) gives a carbonate alkalinity of 50. Lowering the pH to 7.4 will bring the CSI down to -0.12.

I think maintaining a pH of 7.4 should work fairly well.

To lower the cyanuric acid level, you could add and drain water at the same time. Set up a garden hose siphon and begin adding water at the same rate to maintain a consistent level.

Alternatively, you could add 30 to 50 ppm of bromide from sodium bromide to convert to bromine. Bromine's effectiveness will not be reduced by cyanuric acid.

You can use bleach and/or MPS to activate the bromide to bromine. Bromine tabs are not necessary. You can operate a bromine tub just by adding bleach on a regular basis.

To get a more accurate cyanuric acid test, you could dilute the sample 1:1, or more, and multiply the test result by the dilution factor.

For example, if you used 2 parts tap water mixed with 1 part hot tub water, you would multiply the result by 3 to get the actual number.

[hrustar]

I love you folks. This is really helpful information. Thanks for taking the time. I'll review this all in detail and put a plan into action tonight.

[hrustar]

Okay, quick question about lowering my TA.

My product lowers TA and PH. I'd rather adjust them separately.

I intend to use .4 oz of muratic acid to reduce my PH per the pool calculator.

What should i use to reduce the TA and how much? The pool calculator says "To lower TA you reduce pH to 7.0-7.2 with acid and then aerate to increase pH." Not sure I understand this. Does aerate mean run with pumps on? How is that any different than just using my spa?

FYI, I also plan to add 3.3 oz of bleach per the pool calculator to correct my FC levels. My tub is 425 gallons.

[quantumchromodynamics]

I wouldn't worry about lowering your alkalinity. Just add the acid to lower the pH, and the alkalinity will take care of itself.

If your pH goes back up, just lower it back down. After a few times, the pH will stop rising and it will stay where you put it.

Have you had a chance to do a diluted cyanuric acid test? When using chlorine, it is important to know your cyanuric acid because the chlorine level needs to be determined based on the cyanuric acid level.

Adding 50 ppm boron as boric acid/borates would also help you maintain a more consistent pH with less rise.

[quantumchromodynamics]

Calcite is a form of calcium carbonate. The Calcite Saturation Index is a measure of how saturated the water is with calcium carbonate.

Total Alkalinity is a measure of multiple components that can accept hydrogen ions until the pH reaches 4.5. Those components can be such things as Carbonates, cyanurates, phosphates and borates.

The only component of the total alkalinity that is used in the CSI calculation is the carbonate alkalinity. To get the carbonate alkalinity, you have to subtract all of the other forms of alkalinity.

At a pH of 7.8, the calculation for the cyanurate portion of the alkalinity is (Cyanuric acid level X 0.35 = 120 X 0.35 = 42). Therefore, your Carbonate Alkalinity = 90-42 = 48.

If you put a total alkalinity of 48 into the pool calculator and a cyanuric acid of 0, you get about the same number as if you put in an alkalinity of 90 and a cyanuric acid level of 120 (CSI = +0.25).

The issue with carbonates is that they can leave the water as carbon dioxide, which raises the pH. Lowering the carbonates will reduce the loss rate of carbon dioxide, which will reduce unwanted pH rise. A carbonate alkalinity of 48 (estimated) should be low enough to prevent excess pH rise due to loss of carbon dioxide.

Note: I just used a cyanuric acid level of 120 since we do not know your actual level. You really need to determine the cyanuric acid level so that you can know what is the right chlorine level you need to maintain to prevent runaway bacterial growth and so that you can determine your actual CSI and carbonate alkalinity.

A low CSI will dissolve any calcium carbonate in the tub or components. The rate of dissolution increases exponentially as the CSI goes more negative. Most tubs don't contain calcium carbonate unless they have grout (as with a tiled tub) or plaster.

A low CSI might increase the loss rate of metals, but this is not proven or conclusive and some metals will probably be more affected than others, if there is any significant risk. Just to be safe, many people avoid a really low CSI.

A high CSI can cause scale in any tub. How high depends on several variables. Unless the tub contains plaster or grout, the CSI should generally be kept slightly negative to prevent scaling. Generally, -0.3 to 0.0 should give good results for most people.

[Nitro]

I wouldn't worry about lowering your alkalinity. Just add the acid to lower the pH, and the alkalinity will take care of itself.

If your pH goes back up, just lower it back down. After a few times, the pH will stop rising and it will stay where you put it.

This is where we disagree. I prefer to speed up the process by lowering TA until pH stops rising. This can be done in a few hours.

The reason is, some people have very high TA levels (300-400). In which case it will take them a long time (if ever) to get their pH stable, without paying attention to TA. Therefore, I find it's better (easier, less trouble) to adjust TA (to 60-80) from the get go, and fine tune over the course of the next few days, weeks.

[quantumchromodynamics]

I agree that if the alkalinity is definitely high then the "Lowering Alkalinity" method is the best way to go.

However, once the alkalinity is close, then adjusting the pH only will slowly tune in the proper alkalinity without overshooting the balance point.

The carbonate alkalinity is what is going to determine the rate of pH rise due to the loss of carbon dioxide.

The poster's carbonate alkalinity is already less than 50 ppm. I think that that's low enough to start fine tuning the alkalinity by only lowering the pH.

[Nitro]

I agree that if the alkalinity is definitely high then the "Lowering Alkalinity" method is the best way to go.

However, once the alkalinity is close, then adjusting the pH only will slowly tune in the proper alkalinity without overshooting the balance point.

The carbonate alkalinity is what is going to determine the rate of pH rise due to the loss of carbon dioxide.

The poster's carbonate alkalinity is already less than 50 ppm. I think that that's low enough to start fine tuning the alkalinity by only lowering the pH.

I think we are pretty much saying the same thing. I just like to track it so I get a handle on where it needs to be. BTW, carbonate alkalinity may need to go as low as 40 to gain pH stability.

[chem geek]

In terms of theoretical equilibrium of carbon dioxide in hot tub water and in air, the balanced TA with pH is as follows, BUT note that this is lower than you would want for most of these TA -- I'm just giving numbers when the pH would be guaranteed to be stable (i.e. no carbon dioxide outgassing) but in practice a higher TA is still somewhat stable up to a point. These TA values assume a CYA level of 30 ppm.

pH 7.5 TA 19

pH 7.6 TA 22

pH 7.7 TA 25

pH 7.8 TA 30

pH 7.9 TA 35

pH 8.0 TA 40

[hrustar]

Big Trouble!

Okay, I've been working my numbers all week and got them to a what I thought was a close to decent spot today:

PH 7.0

TA 75

CH 125

FC 3.5

CC 2.0

Therefore, I added Boratic Acid (Borax) as suggested to achieve 50 ppm. According the pool calculator, I needed to add 24 oz. I did this and oh boy, according to test strips (trying to get a quick read) my numbers blown up.

PH: 9

FC: Near 0

TA 250

CC : not sure

anyone know why?

To adjust, I just added 3 oz. by volume of Dry Acid to lower PH to about 7.3 or so. I also added 3 oz. Bleach to raise the FC.

PLEASE HELP.

[quantumchromodynamics]

Take another look at the pool calculator. It shows the amount of muriatic acid you need to add before adding the Borax.

Boric acid is more pH neutral, so I think that it's a little bit better way to add boric acid/borates.

Borax contains all borates. However, at normal spa pH, most of the boric acid/borates will be boric acid.

B(OH)₄^- --> B(OH)₃ + OH^-

Borates --> Boric acid + hydroxide.

The borates convert to boric acid by releasing hydroxide ions. The hydroxide ions raise the pH and alkalinity.

Most of the alkalinity increase is due to the hydroxides (not carbonates or bicarbonates), therefore, they will be easy to neutralize with muriatic acid.

OH^- + H⁺ --> H₂O