Endless Pool with High Alkalinity

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Jeffm
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High Alkalinity

Postby Jeffm » Mon 15 Oct, 2007 09:44

Well right now I'm just trying to keep the chlorine levels high enough, it's coming out pretty fast. I think I put about half gallon of Chlorox in over the weekend, and I'm still under 5ppm


Alk was down to 160 yesterday, added another pint of Mur, will check when I get home today, but it's certainly working well. Shooting for about 80.
Will take a full reading of everything else once I get there.


chem geek
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High Alkalinity

Postby chem geek » Mon 15 Oct, 2007 13:19

I'm a bit concerned with all that water and chlorine coming out with the aeration in your indoor space. When this procedure is over with, you should be sure to wipe down all exposed surfaces that got wet. I'd hate for the water and chlorine to deteriorate your metal surfaces. Fortunately, the amount of chlorine is low, but what gets left over is chloride (salt) and that plus the water can continue to be corrosive just with the oxygen in the air. So wiping off the surfaces to get rid of not only the water but also the salt would be wise.

Richard
Jeffm
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High Alkalinity

Postby Jeffm » Tue 16 Oct, 2007 09:51

Actually after the first day, I modified my aeration pipe to run under the security cover. You hardly notice any difference now. It seals up the pool about 99%. So there is no condensation inside, and very little added moisture.

The aeration takes quite a bit longer now than it did the first day, but it's well worth the wait.
Jeffm
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High Alkalinity

Postby Jeffm » Wed 17 Oct, 2007 12:45

Took a water sample in, just to check my numbers:

Temp is usually 77F
pH 7.5
Alk 105
CaH 200 ( I thought it was higher)
Phos 500
TDS 1700
CyA 10 (I thought that was higher too)
DPDI 5

Index 0.5

So..I'll probably raise my pH just by using it. Anyway...Just about perfect. The TDS were a bit high he said...probably from all the jerking around I did trying to get the Alk down initially with acid and soda ash.
chem geek
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High Alkalinity and TDS

Postby chem geek » Wed 17 Oct, 2007 12:55

The TDS will be mostly salt -- sodium chloride. You've also got calcium and carbonate, but mostly it's just plain salt. So long as you use CYA in the pool, you should be fine. If you used chlorine without CYA, then you would be overdosing the pool with chlorine and that combined with the higher salt level can corrode stainless steel faster (chlorides inhibit the formation of the passivity layer that protects stainless steel from corrosion) and produces chlorine disinfection byproducts more quickly and oxidizes skin, hair and swimsuits faster. With your indoor pool, you don't need a lot of CYA, but should target an FC level of a minimum of 7.5% of the CYA level to prevent algae formation (though less likely in an indoor pool). If you use an algaecide, such as PolyQuat 60, then you can use a lower FC minimum target of 3% of the CYA level, but make sure the FC is high enough to not run out with usage. Right now, your 5 ppm FC with 10 ppm CYA is too high in chlorine. You can use Dichlor to easily add CYA to the pool since it dissolves readily and adds chlorine as well (i.e. you can use it as a chlorine source for a short time). You can also get pure CYA, but it takes a long time to dissolve, though can be done in a day or two if you hang it in a sock or panty hose over a return.

They reported a saturation index of 0.5, but it's really at -0.2 which is fine. I'm not sure how they are doing their calculation.

Anyway, congratulations on getting the TA lowered. You should find the pH to be more stable. Let us know how things work out.

Richard
Jeffm
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High Alkalinity

Postby Jeffm » Thu 18 Oct, 2007 08:53

They use the Taylor sliding chart thing..I've got one.

Looks like I'm switching back to the tablets (which contain stabilizer), and stopping the bleach for a while.

The pool guy, said that the stablizer level wasn't as important since it's an indoor pool and doesn't get much UV.

I'm going to guess the TDS is high from all the soda ash I was dumping in, initially along with the acid, trying to get the Alk down. I probably put in 10 lbs or so. (Maybe it just seems that much, because I did put in like 20 lbs before emptying the pool)
chem geek
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High Alkalinity

Postby chem geek » Thu 18 Oct, 2007 11:41

Jeffm wrote:They use the Taylor sliding chart thing..I've got one.

Looks like I'm switching back to the tablets (which contain stabilizer), and stopping the bleach for a while.

The pool guy, said that the stablizer level wasn't as important since it's an indoor pool and doesn't get much UV.

I'm going to guess the TDS is high from all the soda ash I was dumping in, initially along with the acid, trying to get the Alk down. I probably put in 10 lbs or so. (Maybe it just seems that much, because I did put in like 20 lbs before emptying the pool)

I've also got the Taylor Watergram (and my spreadsheet matches it almost exactly except at very high temperatures). If I put in your numbers I get a "pH of Saturation" of just under 7.6. Subtracting this number from your pH of 7.5 gives me -0.1 and is different from the -0.2 I calculated only because I used the 1700 ppm TDS whereas the Watergram doesn't adjust for TDS and assumes standard low initial TDS of around 550 ppm. Saltier pools are more corrosive (in the calcium carbonate saturation sense) though the Watergram doesn't account for that. At any rate, I don't know how the pool store got the 0.5 -- try it out yourself on your own Watergram.

Yes, you can use the tablets for a while -- since you've already got them. For every 1 ppm FC added by Trichlor, you will add 0.6 ppm of CYA. Just remember that they are very acidic so you'll be needing to raise the pH. If you want to raise the pH without raising the TA as much, then you can use 20 Mule Team Borax instead of pH Up. You just use twice as much by weight for the same pH rise effect. You could also use Lye (Caustic Soda / Sodium Hydroxide) where you only need 40% as much by weight vs. pH Up (you would need to pre-dissolve the Lye in a bucket of pool water as it usually comes in pellets; then slowly pour over a return flow at the deep end as you would with any chemicals). If you do use pH Up (which is the same as Arm & Hammer Washing Soda -- careful: not the laundry detergent), then you may need to aerate some more to lower the TA.

The pool guy is only thinking about CYA in terms of protecting the chlorine from breaking down from the UV in sunlight. He isn't thinking of CYA as reducing disinfecting chlorine concentration (i.e. being a chlorine buffer with most chlorine in the form of relatively inert compounds) since the industry never talks about that. It could reduce Trichlor/Dichlor sales if people believed they needed to have more control over their pool's CYA level since most sales are to outdoor pools so the mantra is "CYA doesn't matter; only FC matters" which just isn't true. Also, with higher CYA, it's more likely to get algae (unless FC is increased proportionately) so that increases algaecide sales, etc.

At any rate, you probably don't need any more than 20 ppm CYA and can just try and maintain an FC level of 2 ppm if that seems easy enough to maintain (I suspect it will be since there isn't sunlight breaking down the chlorine and your bather load isn't high). I'd be sure to test the CYA level yourself as I've heard of pool stores measuring it inaccurately or subtracting the measurement number from 100!

Yes, the Soda Ash was Sodium Carbonate while the Muriatic Acid is Hydrogen Chloride so the net effect after aeration which removes much of the Hydrogen Carbonate is that you are left with Sodium Chloride (salt).

Richard

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