saltwater pool question

Total hardness and calcium hardness in pool water.
Scale, calcium buildup, hard water and scaling problems.
vin

saltwater pool question

Postby vin » Thu 24 May, 2007 11:54

Hi all - first time poster here.

Just had my pool water analyzed & everything was fine, except the guy said my calcium hardness is low & I have to add 25# of "hardness plus". I seem to remember the same thing happening last year when I opened my pool. I run a saltwater system in my 20,000 gal. inground pool, so I'm wondering if that's got something to do with it. The guy said the calcium is necessary in order to prevent corrosion of my pool heater.

Does this sound right? Don't the salt (softener) & calcium (hardener) have opposing effects on the water chemistry? Will my increasing the calcium hardness have an adverse affect on my chlorine generator?

Thanks for your time!


Buggsw
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Postby Buggsw » Fri 25 May, 2007 20:49

What is your pool surface? Plaster, vinyl, fiberglass, etc?
Guest

Postby Guest » Sun 27 May, 2007 18:39

Pool is vinyl - thanks.
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Postby Buggsw » Mon 28 May, 2007 02:48

You didn't say what your CH test reading is. Is the water in your area considered soft or is your fill water source going through a water softener in your home? I think most areas regular tap water is usually not soft and would be above 140 ppm. You could run a test on yours to find out what your fill water readings are.

The recommendation for a vinyl pool is 80 - 200 ppm, though there are some people that scoff at even worrying about low calcium with a vinyl pool, others argue that proper water balance includes proper levels of CH, regardless. Pool heaters add another element to it.

I don't have a heater, so am not familiar - but I know enough that you don't want to have any increased corrosion in them. I also have read many times that corrosion is caused more often by acidic water (low pH), but yes very low CH can cause it, as well. Too high of CH causes scale, which is also not good for pool heaters.

You might want to check with the heater manufacturer, to get their recommendation.

I found a manual for one pool heater manufacturer online, that says if you have heat exchanger corrosion it voids the warranty. They give a general guide of:

pH 7.6 to 7.8
Total Alkalinity 80 to 120 ppm
Calcium Hardness 150 to 250 ppm
Salinity 4000ppm
Guest

Postby Guest » Wed 30 May, 2007 13:21

Thanks for your insight, Buggsw :) . I didn't ask the guy what the exact number was, but I will next time. I went ahead & added the recommended dosage & all seems well as of right now. The pool is open, balanced & looks great. It's funny though as there seems to be some unsolved mysteries when it comes to saltwater systems. Another little issue that I've been dealing with on mine is the ph constantly creeping upward & every so often I've got to add a few pounds of dry acid. I did some research & it seems to be a common occurance in saltwater pools although no one seems to be able to explain why it happens. I guess until these systems become more mainstream, some of these answers will continue to elude us.
me_too

Postby me_too » Wed 30 May, 2007 18:39

Anonymous wrote: I did some research & it seems to be a common occurance in saltwater pools although no one seems to be able to explain why it happens. I guess until these systems become more mainstream, some of these answers will continue to elude us.

It has to do with production of sodium hydroxide from the cell combined with (nitrogen? I have to look at the equations) outgassing. These elements combine to raise the pH.
Buggsw
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Postby Buggsw » Thu 31 May, 2007 00:26

Yes, I think it is pretty normal to have to use acid a little more frequently.
In fact there is one SWCG that is called AutoPilot Total Control that includes a big tank which dispenses acid along with the system generating chlorine from salt. I'm saving my pennies for that one - I'd love to not have to handle acid manually any more than to refill the tank every so often.

What is your TA? If your TA is too high or too low, you will see greater swings with pH.
Guest

Postby Guest » Mon 04 Jun, 2007 12:06

TA is 90. I also try to be diligent about keeping the pH at the lower end of the scale - around 7.2-7.5. This seems to keep pH creep from getting out of control.

The pool is dialed in pretty nicely right now w/ the SWCG working at only 20% to maintain a chlorine level between 1.0 - 2.0. Although it just rained about 3" last night, so that's probably changed things a bit ;-).

Thanks to all for your comments.
Guest

Postby Guest » Tue 12 Jun, 2007 20:06

Acidic pool chemistry WILL over time breach the inner wall of a copper/cupernickel heat-exchanger (condensor); which results in complete failure of a heatpump (aka its now scrap, a flooded unit). A ph of 7.4 is perfect. However, w/a titanium coil, chemical damage of any type is basically nill. Also, salt content of about 3000 ppm is the same as the human tear, which is perfect.
Griz

saltwater pool question

Postby Griz » Fri 24 Jul, 2009 21:20

To all, I have been a proud owner of a beautifu vinyl 20,000 gal salt water pool for 2 years.
Two days ago I had my water tested at the local pool suply store. All the chemistry was in ballance except I was told my water softness was to low 120 ppm. The clerk said to add at least 25# of water hardner. I did some research and learned the pool hardness should be between 200 - 400 ppm. I proceeded to add 35# of hardner which should bring the pool to near 250 ppm. Befoe I added the hardner my CH was 2.5 . After I added the hardner the CH measured 1 . I have been strugling to get the CH back to 2.
It's almost as if my generator stoped making CH. Although I can measure higher levels of CH pumping at the returns. I am concerned the hardner has changed my pool chemistry and would like to know how I can get it back to normal.

Thanks for any response.
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saltwater pool question

Postby chem geek » Fri 24 Jul, 2009 22:52

Just so you know, "CH" stands for Calcium Hardness and what you meant was "FC" for Free Chlorine. What is your Cyanuric Acid (CYA) level in your pool? You should just add extra chlorinating liquid or 6% unscented bleach to raise the chlorine to a higher level since you probably have some nascent algae growth. The calcium by itself would not have done anything to the chlorine generation unless it was so high that it caused scaling in the salt cell itself. If your water got cloudy, then that is possible. You can use 50 ppm Borates to reduce the possibility of scaling.

By the way, the pool store was wrong to advice you to increase your Calcium Hardness since you have a vinyl pool that doesn't require saturation with calcium carbonate.

Read Water Balance for SWGs and Shock Your Pool.
gasman

saltwater pool question

Postby gasman » Sat 12 Dec, 2009 08:39

re. the climbing ph problem in salt polls mentioned earlier,my experience was that 150 mls (approx a third of a gallon) of acid was required weekly to maintain the ph level,until I painted the concrete shell.Since then no acid has been required for many years.
When the pool was refilled,rainwater and carbon filtered water was used,giving a zero CH level.This was great,no cleaning of the cell,pool was clean,etc. under advice I have added calcium and used calcium hydrochloride to raise the CH ,now I have to sink a lot of granular acid to dissolve the brownish scale that covers the paint.
whats the difference between a vinyl or fiberglass pool and a well painted concrete one.
czechmate
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My Pool: 16 x 32 gunite21000 gal., Diamond Brite Blue, Swimquip XL pump, DE36
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saltwater pool question

Postby czechmate » Thu 17 Dec, 2009 16:48

I would like to caution any gunite pool owners, who have this "problem with pool requiring acid weekly", as stated in article above, to think not twice. but ten times before painting their plaster.
It is lot cheaper to learn the reason for PH unbalance then draining, acid-washing and painting to have a result that may last for 5 years at best.
If done by the ever present "poolpainters" it will be peeling in 3 years.
To this present time, lasting paint that will adhere and last, is still waiting on the drawing board.
m-nahorn

saltwater pool question

Postby m-nahorn » Wed 02 Jun, 2010 19:28

my pool is 2 years old and at the lower end of the steel wall started to rust and bled thru my liner and put a hole in 2 spots with in 4 feet of each other the pool company repaired them now this year same thing about 4 feet over same location at bottom of steel wall.if you rub the liner on the ohter side you can feel lumps under liner like corrsion is forming there also but not leaking thru

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