Endless Pool with High Alkalinity

[Jeffm]

Mr. C,

Thanks for your input, but I don't have the secondary pump. Didn't get the jacuzzi option.

If you're thinking of the power unit that generates the flow. Yes, that does really move the water, but the 6HP hydraulic pump in the basement makes a bit of noise (working on enclosure).

Really the best option is a little PVC pipe I've already drawn up, and just putting that on the return fitting. Less power consumption and alot quieter.

I do have a float....and had the tabs in there from time to time, but I think I'm switching to the bleach, and will just use the float when I'm going out of town etc..

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[Jeffm]

Well, I'm not done yet...but I must say that the rate at which pH increases with good aeration is impressive. I went from 7.2 to 7.8 in like 3 hours.

The downside is a very humid room...

Looking forward to putting more time into this tonight.

[chem geek]

Too bad about the humidity. I didn't think about that since most pools are outdoors so the aeration doesn't have such side effects. The pH rise is fastest from the lowest pH -- so faster from 7.0 to 7.2 than from 7.6 to 7.8 -- so you can add acid whenever it goes up or just at regular intervals, whatever is convenient for you. The amount of acid it takes to lower the TA is independent of how frequently you add it or how far you let the pH go up between additions -- adding the acid before the pH goes up a lot just makes the process go faster but doesn't change the cumulative total amount of acid needed.

In 3000 gallons, every 100 ppm reduction in TA needs a cumulative total of 77 fluid ounces of Muriatic Acid (31.45% Hydrochloric acid) though you obviously don't add that all at once since you don't want the pH to go below 7.0. That should give you some idea of how you are doing and how much you'll need -- assuming the TA test was accurate.

To go from a pH of 7.5 to 7.0 at a TA of 400 requires 33 fluid ounces of acid and will lower the TA by 44; at a TA of 300 it requires 26 fluid ounces and will lower the TA by 33; at a TA of 200 it requires 18 fluid ounces and will lower the TA by 23; at a TA of 100 it requires 10 fluid ounces and will lower the TA by 13. That should give you a rough idea of what is required as your TA gets lower. I'm sure you'll get a feel for this as you proceed. You can see how it will take more frequent acid addition as you get to lower TA and you'll also find that the pH rises more slowly at lower TA (which is what you're really trying to get to). You could probably just get down to 80 and stop there and see how things go in terms of pH stability. I only mentioned 50 before thinking that your pool had a lot of aeration, but then realized you had high TA from the Soda Ash.

Richard

[Jeffm]

Well,l I was down to 250 ppm last night.

I modified my aerator pipe, so it fits underneath the cover. So, I can keep the humidity contained. The aeration and pH rise is much slower now. (I expected that) but wow...every surface of the inside of my sunroom has water on it from the previous night.

I also found another side effect of the aeration. Algae formation. Cl levels were about 3 ppm. I put in 1 cup of bleech for now, and guess I'll address the algae when I get done with the Alk.


Running the pump all day should get the pH way up again so I can put more acid in tonight when I get home.

[chem geek]

The aeration probably outgassed the chlorine faster as well, so yes, the chlorine level needs to be kept up or else algae can form. Too bad you can't aerate the water and get the TA lower before it gets added to your pool.

I wouldn't wait to address the algae. I'd hit it with chlorine now or else it will just get worse.

[Jeffm]

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]

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]

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]

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]

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]

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]

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