How much salt does liquid bleach add?

[smallpooldad]

How much salt does liquid bleach add to a non-SWG 10,000 gal pool, if one adds 2 ppm every day.

Does it add calcium or is this because of adding 8 oz of acid daily? This might help, we also add 20 ppm baking soda every 3rd day.

Any help would be appreciated from you chemistry types, or am I completely off base?

Looking forward to the replies

[chem geek]

If you add enough liquid bleach to add 2 ppm of chlorine to your pool, then you are adding 2.2 ppm of salt (NaCl) -- remember that the "ppm" is parts-per-million (weight fraction) or equivalently milligrams-per-liter so the "ppm" number is dependent on the weight of the substance. The 2 ppm of chlorine refers to HOCl which weighs a little less than salt. When you add NaOCl (sodium hypochlorite, or bleach) that makes Na+ and OCl- some of which converts to HOCl. Then, the HOCl and OCl- get used up over time and produce Cl- (the H+ goes to water if you are maintaining pH) and the "O" leaves as oxygen gas or goes to water (depending on what the chlorine reacts with).

There is no calcium added. Adding acid will add chloride ion (Cl-) if you are using muriatic acid or it will add sodium (Na+) and sulfate ion (SO4(2-)) if you are adding sodium bisulfate. However, if you are using bleach, you normally do not need to add any acid because the increase in pH from adding bleach is temporary since the "using up" of chlorine is an acidic process so the net result of adding chlorine and having it used up has no net change in pH (technically, there is a small rise in pH due to extra sodium hydroxide, or lye, that is added to or left in the bleach to keep it more stable by increasing its pH -- the amount of TDS from this extra base is only 0.1 for the example you gave so is negligible). See the post on pH for more information.

You shouldn't need to add baking soda that often either. It sounds like your situation is one of rising pH, then adding acid to lower the pH but that lowers the alkalinity too, and then adding baking soda to raise the alkalinity. Something is wrong in your pool system -- either the chemistry is not in good balance (pH is too low, alkalinity is too high) or the water is getting aerated too much or both. Can you give us the full set of numbers, if you have them, at a single point in time?

FC (free chlorine)
CC (combined chlorine -- total chlorine minus free chlorine)
pH
TA (total alkalinity)
CYA (cyanuric acid)
CH (calcium hardness)
Temperature

Also, is your pool open without a cover? Do you have water features -- fountains, water slides, etc.? Is the pool used a lot and is there a lot of splashing that goes on (i.e. kids, or adults who remember what it's like to be a kid )?

Thanks,
Richard

[thewayne]

So.... How much salt does liquid bleach add?

[waterbear]

chem geek answered that in the first line of his post, for every 1 ppm bleach you are adding 1.1 ppm salt!

[smallpooldad]

Dear Richard (Chem Geek),

Thank you for your reply here are the numbers.

9,000 Gal Gunite pool
Pump Runs 12 hours
Sunlight 12 hours per day with high UV

FC 6 lowering to 4 at end-of-day (Wal-Mart's Ultra Bleach 6%)
CC 0
pH 7.3 rising to 7.5 at end-of-day (Muriatic Acid)
TA 100 lowering to 80 after 3 days (with CYA/Alkalinity allowance of minus 20 therefore TA reads 120 and lowers to 100) (using Baking Soda)
CYA (cyanuric acid) 50
CH (calcium hardness) 250 (rises 70 ppm after 3 months)
Temperature 80 F
Salt 1400 ppm no saltwater generator pool (not sure of the rise after 3 months but will advise in 3 months)

The pool is open without a cover, no water features, it is not used a lot only by me - no splashing.

We do have a lot of trade winds blowing 15 to 25 mph. These winds blow in fine airborne dust and pollen and a fair amount of leaves which I remove daily. They also blow in red dirt, aka ferric oxide or rust if you like, from the volcanic soil; this creates an iron issue. I treat this every month with one quart of Omni's stain control (not remover). Water is topped of with 160 gals once or twice a week depending on how windy it has been.

Could the blow-in be affecting the balance or is it possible that the rains which travel far over the Pacific ocean have a different chemical composition from those on the mainland USA, such as more salt?

When it rains the pH rises and the alkalinity drops.

My neighbours pool has exactly the same results as ours except that their pool is 20,000 gals gunite.

Tap water in Hawaii is pH 7.9, Alk of 60, hardness of 60 ppm, no chlorine.

Hope this helps and looking forward to your reply.


Aloha.

[chem geek]

First of all, why is your calcium rising? You don't seem to be adding anything that would increase calcium (such cal hypo for chlorine -- you are using bleach).

As for the other parameters, I can reproduce what is going on in your pool by assuming the following (converted to the equivalent as if it were done every day):
ACID: You add 8 ounces of muriatic acid per day PLUS there is an additional equivalent of 10.5 ounces of muriatic acid that is probably coming from the rain.
BUFFER: You add 14.6 ounces (weight) of sodium bicarbonate every day. This is equivalent to the amount needed to raise alkalinity by 20 ppm over 3 days.
OUTGAS: You are outgassing about 5.5 moles (about 8.9%) of your total carbonate in your pool).
CHLORINE: You are adding enough chlorine equivalent of 2 ppm per day. I also assume that this same amount is used up through normal processes each day.

It makes sense that your alkalinity drops faster with rain since the raindrops probably churn up the water and increase the rate of outgassing and you have a lot of that due to the wind anyway. When you say that during rains the acidity rises faster, did you mean the pH rises faster (which is actually more basic, not acidic)? If so, then that doesn't make as much sense since there appears to be more acid getting added to your pool from some source beyond what you add because your pH is not rising as much as it should just from the outgassing (alkalinity change).

If you are getting lots or rain, then I would expect all of your parameters, including calcium and alkalinity, to drop from dilution. Again, the rising calcium is a strange thing.

Anyway, there doesn't seem anything terribly wrong with your situation. When you have a pool exposed to the environment, you're going to be at the mercy of that environment. Only a pool cover that would keep the rain out would help.

That's my two cents.

Richard

[chem geek]

P.S. to last post.

Your increase in calcium may be due to the water you are refilling since it does have some hardness to it, but I didn't run through the calcs to see if that explains it all. When water evaporates, it just concentrates what's in the pool so if you add pure water you get back to where you started, but when tap water has something in it, then it gets added to what's already in the pool. It's possible the rain may add some hardness -- you could test your rain water to find out and also test it for salt which, as you surmise, may be where the salt is coming from (normally rain doesn't have salt, but maybe the winds mix up sea spray with rain during storms -- who knows, just test it to find out).

At any rate, a pool cover would also cut your evaporation and generally stabilize your pool. Other than that, I don't have anything to suggest except enjoy the pool!

[chem geek]

Another thought. Since you seem to be having a lot of outgassing of carbon dioxide, you might consider running your pool at higher pH and lower alkalinity, say start at 7.4 or 7.5 and lower alkalinity to 80. See if you still get the same amount of pH rise and alkalinity drop (after adding acid to restore the pH) as you do currently. If it's better, then this is an option for you.

The relationship between carbon dioxide outgassing is shown in the following link (CO2.png) where you can see that there is a rather large change in the relative rate of outgassing from a change in pH and a lesser dependence on alkalinity. The difference between pH 7.3 and Alk. 100 (relative outgas rate 20) and pH 7.5 and Alk. 80 (relative outgas rate 7) is almost a factor of 3 difference which may be enough for the 7.5 and 80 combination to be stable enough for you to live with. At least it's worth a try and with your current situation it should be easy enough to see how it goes. Of course, you may still bounce in pH from 7.5 up to 7.6 but you may not need to add as much acid as before.

If you try this, be sure to report back your results. I'm trying to see what sort of relative outgas rates are "tolerable" in different situations. Right now you'll see the "Limit" line in the graph at around 15, but this is somewhat arbitrary and dependent on the amount of aeration (and you have quite a lot due to the wind and rain).

Richard

[smallpooldad]

Wow,

I am so impressed with your knowledge and even more with your kind help.

I will try all you suggested and report back. For the next few days I am removing iron stains and will be draining the pool on Thursday or Friday.

One last thing I did a phosphate test before the iron treatment and it was beyond a 1000 ppb, most probably airborne pollution and leaves falling from a nearby tree which I net out daily. I wonder if this level could cause problems? I have no algae issues but I will now use a phosphate remover from SeaKlear to control this, do you have any opinions on this?

Aloha,


Paul

[smallpooldad]

Ok,

If we lower the Alk to 80 should we use a CYA adjustment for 50 at 7.5?

In other words should the indicated Alk on the test be higher?

Aloha