I have a saltwater pool and didn't even know it...

[Titanium]

While buying some refills for dpd powder and dpd-FAS reagent from tfttestkits, I decided to buy the Aquacheck salt strips. I don't have a saltwater pool and I have never added an ounce of salt. I am thinking about adding a SWG next year, but wanted to get an idea of my base salt level due to my use of liquid chlorine over the last couple of years.

The white peak on the test strip reached 4.4, which according to the chart on the back of the bottle is a salt level of 1630 ppm.

Does this level seem in the range of being reasonable considering:

1. bought house in early 2006.
2. have a cartridge filter - so no backwashing
3. replaced 40% of water last year due to high CYA
4. Typically use 3-5 gallons of 10% chlorine per week in the summer, dropping to 1-2 gallons per month in the winter (if that).

I don't typically notice any whitish salt deposits on the deck after the water evaporates, although we have an aggregate deck so it might be really hard to notice.

I'm just having a hard time with the fact that I'm already 50% of the way to a saltwater pool without having added any salt. (I realize that adding liquid chlorine adds some salt for every ppm of chlorine added.)

I've always been a bit worried about the extra corrosion going from a freshwater pool to a saltwater pool, but if I'm really at 1630 ppm, roughly doubling that number to 3500 ppm doesn't seem so scary anymore.

 

[chem geek]

3-5 gallons of 10% chlorinating liquid per week in 24,000 gallons is 12.5 to 21 ppm FC per week. For every 10 ppm FC, ALL sources of chlorine result in 8 ppm salt since the chlorine converts to chloride, but most hypochlorite sources of chlorine add an additional 8 ppm salt that is already in the product. So, you have been adding 20 to 34 ppm salt per week during the summer. That's 520 to 884 ppm over 6 months so your salt levels are certainly plausible given multiple seasons and some dilution but not very much since you have a cartridge filter. Also, plaster pools typically start off with around 500 ppm TDS due to the calcium chloride that is initially added for CH and the sodium bicarbonate sometimes added for TA.

I also have a cartridge filter and minimal dilution so I use winter rains to dilute the water and keep salt levels from rising too much, though I intentionally didn't do that for a few seasons to see what a higher salt level would feel like. I'm now going back to winter dilution since my wife didn't notice much difference.

 

[reebok]

I was surprised when I found out my salt was 1800. I was going to add some for the benefits people talk about, but it turns out I already had more salt in my pool than I was planning on adding! mine was refilled in 12/07. I have always used liquid chlorine, though moreso now that I found this site and ditched the evil tabs.

 

[frustratedpoolmom]

Yes, this is a good example of why we tell folks to test for salt BEFORE adding it for a new SWG as most if not all pools will have some salt and they don't want to overshoot and end up too high.

I wonder what my level is....

 

[Butterfly]

I also plan on ordering the salt strips from Dave next time for the same reason as Titanium.

My water feels so soft :-D

 

[Guest]

I also plan on ordering the salt strips from Dave next time for the same reason as Titanium.

My water feels so soft :-D

Salt does NOT soften water! It has NO EFFECT on either calcium or magnesium hardness. Salt is used in a water softener to recharge the ion exchange resin, which is what softens the water by exhanging sodium or potassium ions for the calcium, magensium, and other metal ions in the water.

The subject 'better water feel' that people notice after adding salt is because the water is closer to the salt level in the cells of the body so the water is less 'aggressive' and creates less osmotic pressure. (In other words, your toes won't get as"'pruney" when you soak.)

 

[Titanium]

3-5 gallons of 10% chlorinating liquid per week in 24,000 gallons is 12.5 to 21 ppm FC per week. For every 10 ppm FC, ALL sources of chlorine result in 8 ppm salt since the chlorine converts to chloride, but most hypochlorite sources of chlorine add an additional 8 ppm salt that is already in the product. So, you have been adding 20 to 34 ppm salt per week during the summer. That's 520 to 884 ppm over 6 months so your salt levels are certainly plausible given multiple seasons and some dilution but not very much since you have a cartridge filter. Also, plaster pools typically start off with around 500 ppm TDS due to the calcium chloride that is initially added for CH and the sodium bicarbonate sometimes added for TA.

I also have a cartridge filter and minimal dilution so I use winter rains to dilute the water and keep salt levels from rising too much, though I intentionally didn't do that for a few seasons to see what a higher salt level would feel like. I'm now going back to winter dilution since my wife didn't notice much difference.

chem geek,

Thanks for the great answer. So my salt levels reading is within a reasonable range. That is great to know.

I'm a little confused by you mentioning the calcium chloride and sodium bicarbonate. Are you saying that the Aquacheck salt strips are reacting to more than just sodium chloride? If yes, would I adjust the salt strip number by subtracting the CH and TA numbers in order to reach a true sodium chloride number?

Regarding keeping your salt levels lower: are you doing this to minimize corrosion effects?

 

[Guest]

I'm a little confused by you mentioning the calcium chloride and sodium bicarbonate. Are you saying that the Aquacheck salt strips are reacting to more than just sodium chloride? If yes, would I adjust the salt strip number by subtracting the CH and TA numbers in order to reach a true sodium chloride number?

The strips are a chemical test for chloride ions in the water, not for salt per se. It does not matter if the chlorde ions come from sodium chloride, calcium chloride, or breakdown of chlorine. Sodium ions are added to the water with sodium bicarbonate. When you have sodium and chloride ions in the water you have salt in the water.
You make no adjustments to the reading on the strips since the chloride reading is what you want. You could add potassium chloride to the water and it will also register on the strips, btw.

 

[JasonLion]

Almost every one of the common pool chemicals adds some salt to the water. Salt levels in a newly filled pool start around 300 or 400 and over time will rise up as high as 2,000.

 

[Titanium]

Jason and waterbear,

Thanks for the clarification. So chloride is what the strips measure, and chloride ppm is the reading I want when/if I take the SWG plunge.

So much for the saltwater vs no-saltwater debate.

Seems to me there is a lot less difference between a 2000 ppm "freshwater" pool and 3500 ppm "saltwater" pool (less than 100% increase in salt ppm) than between a 0 ppm freshwater pool (I didn't realize there was no such thing) and a 2000 ppm "freshwater" pool (infinite % increase in salt ppm).

 

[anonapersona]

Trying to stay on topic here... so with a freshwater pool and rising salt levels due to bleach and other chemical additions, at what point do you begin to worry about causing rust to metal parts near the pool?

When we were house shopping I visited on house with a saltwater pool and the back door, metal, had bad rust on it. I'd like to avoid that in this house and though I have not tested, I suspect the salt level is rising given the bleach consumption rate this summer.

 

[The Mermaid Queen]

Trying to stay on topic here... so with a freshwater pool and rising salt levels due to bleach and other chemical additions, at what point do you begin to worry about causing rust to metal parts near the pool?

When we were house shopping I visited on house with a saltwater pool and the back door, metal, had bad rust on it. I'd like to avoid that in this house and though I have not tested, I suspect the salt level is rising given the bleach consumption rate this summer.

We had a home with no pool, salt or otherwise, and our back door was also rusted. There are many factors that cause oxidation (rusting) of metals, not just salt!

 

[chem geek]

So chloride is what the strips measure, and chloride ppm is the reading I want when/if I take the SWG plunge.

So much for the saltwater vs no-saltwater debate.

Seems to me there is a lot less difference between a 2000 ppm "freshwater" pool and 3500 ppm "saltwater" pool (less than 100% increase in salt ppm) than between a 0 ppm freshwater pool (I didn't realize there was no such thing) and a 2000 ppm "freshwater" pool (infinite % increase in salt ppm).

Just to be technically accurate, the strips measure chloride, but the reading they report is in units of ppm sodium chloride, or basically standard table salt. So if you were to weigh salt to be added to the pool to achieve the same chloride level, the ppm number would directly relate to that weight.

As for corrosion rates, it's not exactly linear though is approximately so due to conductivity being roughly proportional to TDS level. Also, corrision depends on multiple factors. Nevertheless, with everything else equal, higher TDS levels will corrode metal faster. This only becomes noticeable if less corrosion-resistant metals are used. An exception to this roughly linear effect is the effect of chlorides specifically (not TDS in general) on stainless steel (and probably aluminum). For these metals, which rely on a passivity layer for protection, higher chloride levels can interfere with this process and lead to a runaway corrosive effect. In practice, we've only seen this occur when the salt level was at SWG levels (i.e. 3000 ppm) AND the pool water had fairly high chlorine (3-5 ppm FC) with no CYA in the water (i.e. some indoor pools).

Richard