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My Water Stats - Advice Please


Razorhog

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I've only had the tub for 3 days now, but I wanted advice on the water chemistry. My TA is 200, CH is 120, PH seems to stick at 7.8. I put in enough dichlor to get to 4ppm FC before a soak, and after I do the same. Each morning FC has been around 2. I've only put in about 2 oz of dichlor so far, and CYA is not detectable yet.

First fill the dealer had me put in a cap of SpaGuard Shock (dichlor), 7 cap fulls of SpaGuard "Stain and Scale Control", and a quart of SpaGuard "Spa Sentry" (ph Buffer - K2HP04).

They did not send any pH down or pH up.

The water is terrific right now - very clear, soft, no foam with jets on. If the PH does not go above 7.8, is there any reason to be concerned about the total alkalinity being at 200?

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That stuff is the mnost common PH down, sodium bisulfate, it works just fine, it will lower alk and PH, fairly safe to handle compared to Muriatic Acid.

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I've only had the tub for 3 days now, but I wanted advice on the water chemistry. My TA is 200, CH is 120, PH seems to stick at 7.8. I put in enough dichlor to get to 4ppm FC before a soak, and after I do the same. Each morning FC has been around 2. I've only put in about 2 oz of dichlor so far, and CYA is not detectable yet.

First fill the dealer had me put in a cap of SpaGuard Shock (dichlor), 7 cap fulls of SpaGuard "Stain and Scale Control", and a quart of SpaGuard "Spa Sentry" (ph Buffer - K2HP04).

They did not send any pH down or pH up.

The water is terrific right now - very clear, soft, no foam with jets on. If the PH does not go above 7.8, is there any reason to be concerned about the total alkalinity being at 200?

You should look at your CSI index. Calcium, TA, and pH are major components of the index. Usually, you shoot to get as close to zero as you can.

When I put your numbers into the pool calculator, I get a value of near 0.5. This is within range, but certainly far from ideal. I suggest that you use the pool calculator and put your numbers into it and see what you get. You might want to adjust your CSI to get closer to zero. (My calculation might be off because I don't have all your numbers.)

The CSI index tells you how likely you are to have scale/calcium related problems in your pool/tub. A number close to zero is preferred.

Good luck,

- Simon

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I've only had the tub for 3 days now, but I wanted advice on the water chemistry. My TA is 200, CH is 120, PH seems to stick at 7.8. I put in enough dichlor to get to 4ppm FC before a soak, and after I do the same. Each morning FC has been around 2. I've only put in about 2 oz of dichlor so far, and CYA is not detectable yet.

First fill the dealer had me put in a cap of SpaGuard Shock (dichlor), 7 cap fulls of SpaGuard "Stain and Scale Control", and a quart of SpaGuard "Spa Sentry" (ph Buffer - K2HP04).

They did not send any pH down or pH up.

The water is terrific right now - very clear, soft, no foam with jets on. If the PH does not go above 7.8, is there any reason to be concerned about the total alkalinity being at 200?

You should look at your CSI index. Calcium, TA, and pH are major components of the index. Usually, you shoot to get as close to zero as you can.

When I put your numbers into the pool calculator, I get a value of near 0.5. This is within range, but certainly far from ideal. I suggest that you use the pool calculator and put your numbers into it and see what you get. You might want to adjust your CSI to get closer to zero. (My calculation might be off because I don't have all your numbers.)

The CSI index tells you how likely you are to have scale/calcium related problems in your pool/tub. A number close to zero is preferred.

Good luck,

- Simon

You are right, CSI is .52 I'll lower TA tomorrow to get it closer to 0. Looks like I'll need a TA of around 100, and pH of 7.5. That would give me a CSI of .06

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The Total Alkalinity is composed of multiple components, including carbonate, cyanurate, borate and phosphate. The CSI calculation uses only the carbonate portion of the TA. The pool calculator has a correction for cyanurate and borate when entered in the boxes. It does not correct for phosphate.

To get the correct CSI, you need to subtract the phosphate component of the TA.

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Ok - I'm confused about the amount of dry acid it will take to lower the TA. I've read here that in a 350 gal tub, 8 oz of Dry Acid will lower TA by 100ppm. I have a 539 gallon tub, and the pool calculator does not say how much acid to add in order to lower TA. It says I need 5.4 oz by weight of dry acid to decrease pH from 7.8 to 7.0. Should I slowly lower pH to 7.0 and then aerate to bring pH back up?

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Here is the post about lowering TA. However, before you do, you need to subtract the phosphate component.

Spa Guard Spa Sentry is listed as Phosphate Buffer 36.3 %, with a specific gravity of 1.36 grams per milliliter.

1 quart = 946.4 milliliters = 1,287.1 grams total product = 467.2 grams of phosphate.

pKa for phosphoric acid:

pKa1 =2.15, pKa2 = 7.21 and pKa3 =12.34

Since the product is listed as pH neutral at a pH of 7.5, then 66 % should be in the form of Dipotassium phosphate (K2HPO4) and 34 % should be in the form of Monosodium phosphate (NaH2PO4) on a molar basis.

[edit]The mix might contain monopotassium phosphate instead of monosodium phosphate. Either way, the correction is about the same. For example, at a pH of 7.8, the correction factor would be 57 ppm instead of 59 ppm.[end edit]

There should be 2 moles of Dipotassium phosphate (K2HPO4)) (174 grams per mole x 2 = 348 grams) and 1 mole of Monosodium phosphate (NaH2PO4) (120 grams per mole). 348 grams + 120 grams = 468 grams.

Since there are 3 moles of phosphate ions, at a pH of 7.8 about 80 % will be in the form of HPO42-. That makes 2.4 moles of HPO42-. TA is reported in units of calcium carbonate equivalent. 2.4 moles of HPO42- equal 1.2 moles of calcium carbonate. Calcium carbonate is 100.1 grams per mole x 1.2 moles = 120 grams CaCO3. 120 grams CaCO3 in 400 gallons of water = 79 ppm.

Volume.............subtract from TA

300 gallons............105 ppm

350 gallons............. 90 ppm

400 gallons..............79 ppm

450 gallons..............70 ppm

500 gallons..............63 ppm

MSDS

In your case, if your tub is 539 gallons, then you should use a TA of 200 - 59 = 141 ppm in the pool calculator.

Since you have added 2 ounces of dichlor, then your cyanuric acid should be about 14 ppm. Cyanuric acid does not always register very well below 20 ppm. You should assume that you have 14 ppm of Cyanuric acid and enter that into the box for cyanuric acid.

Typically, when lowering TA, you want to lower the pH to about 7.0 using muriatic acid, and then aerate to raise the pH. Keep doing that until the TA is correct.

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Quantum - brilliant post, thank you! After taking phosphates into account, it shouldn't take me too long to get the TA down. Next fill I plan on using boric acid as a pH buffer, rather than Spa Sentry, which will hopefully make calculations easier. Is it safe to assume that I need to subtract 59 ppm from TA for every testing until a fresh refill?

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The correction factor depends on the pH. As long as the water is not diluted, then you should apply the following correction factor.

pH................correction factor

7.0......................29 ppm

7.1......................33 ppm

7.2......................36 ppm

7.3......................41 ppm

7.4......................45 ppm

7.5......................49 ppm

7.6......................53 ppm

7.7......................56 ppm

7.8......................59 ppm

7.9......................61 ppm

8.0......................63 ppm

If the water is diluted, then you would use a smaller correction factor based on the percentage of water dilution.

Here is a good source for boric acid.

If the tub has any cement, such as from grout or plaster, then the CSI should be kept at about 0.0. If there is no cement, then the CSI should be kept at -0.2 to -0.1 to protect the heater element from scaling. If the heater element gets a coat of scale, it will overheat and rupture. Calcium carbonate gets less soluble as the temperature increases.

The phosphate can also create scale, especially as CaHPO4. This scale can create a substrate that encourages the formation of calcium carbonate scale. Therefore, you should be extra careful to avoid a positive CSI. Maintaining a -0.3 to -0.2 is fine as long as there is no grout or plaster.

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wow - am I missing something or are you guys making this harder than it needs to be?

LOL, maybe so, but it is what it is. All of the actual chemistry is above my head, but I still need to know what to do in order to get the water balanced and sanitized. I've read enough to develop a pretty good understanding of what to do, and once I "get to know" my tub and water, a routine will settle in. I suppose water maintenance can be as complicated as you want it to be. I have no desire for it to be tedious, yet I feel like I should know what I'm doing because good water quality is important for both the tub and bathers' health. Clear water is not necessarily good water.

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One thing I forgot to add - the dealer had me put a "Proclear" mineral spa sanitizer (main ingredient is Metallic Silver) in the compartment with the filter. Do I even need this? I thought a mineral sanitizer was for low-chlorine systems that mainly use MPS.

Can anyone chime in on this?

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