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
Pool Care Proficient
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Posts: 31
Joined: Mon 08 Oct, 2007 11:03

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
Pool Industry Leader
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Location: San Rafael, California

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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