Cal-Hypo Alternative To Bleach

[jakenz]

So i was down at the spa shop today, and got talking to the guy who runs the place rather than the guy who usually runs the tests for me and i explained the system i was running to him, dichlor then bleach, with borax. After initially telling me that only idiots use liquid chlorine because of the shelf life and weight, and i explained that with the use our spa gets, dichlor builds us the cya too quick, lithium is too expensive and cal-hypo increases hardness.

He then told me what they do, add a quanitiy of cal-hypo to water, mix, half an hour later mix again, then leave for a week is a cool dark spot, the calcium settles to the bottom or on top, and you can take the green chlorine solution and leave the calcium behind, dilute this to the to the right strength, ie 6% and you are sorted.

Now for me this sounds very attractive as the strongest bleach i could find that i could use for the spa was 3% and expensive, and liquid chlorine is $30 for 5l around here, unless i buy 20l at a time.

Any thoughts on this method?

[chem geek]

Clorox bleach is now 8.25% and used to be 6%. Most off-brand Ultra bleaches are 6%. Only off-brand regular bleach is 3% (and such bleach tends to have more excess lye in it so makes the pH rise more). Where are you located that you can't get either chlorinating liquid or 6% bleach -- I thought in another post you said you were using "liquid chlorine" because you couldn't find good bleach? Also, the guy is wrong about it not lasting -- bleach lasts quite a long time. It's higher concentration chlorinating liquid that doesn't last as long, though this is very temperature dependent. See the table at the bottom of this link to see that lower concentrations at reasonable room temperatures lasts a long time.

As for making your own bleach from Cal-Hypo, that makes no sense. Calcium hypochlorite in a smaller quantity of water will not completely dissolve since the water can become saturated with calcium hypochlorite since it's solubility (in distilled water) is 210 grams per liter. So if it precipitates and settles, what remains will still be saturated calcium hypochlorite so will still raise the calcium level. The only way that the calcium will be lowered relative to chlorine is if some of the precipitate is calcium carbonate, but the 210,000 ppm of saturated calcium hypochlorite is far higher than the perhaps 80 ppm or so Total Alkalinity that might precipitate as calcium carbonate. With Cal-Hypo, for every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it increases Calcium Hardness (CH) by at least 7 ppm.

[jakenz]

Im not very knowledgeble on the subject, but with a quick internet search i came across this

https://confluence.cornell.edu/display/AGUACLARA/Calcium+Carbonate+Settling+Observations

It seems to support what i was told in the shop?

Im in New Zealand, and the best i could find with an internet seach was budget premium bleach at 4%, but could not find it where it was claimed to be stocked.

That link about the shelf life of liquid chlorine was very informative, thanks for that.

[chem geek]

Like I wrote, you can precipitate calcium carbonate, but the amount is limited by the amount of carbonates in the water. I didn't say it couldn't happen, but that it isn't practical for significantly reducing the amount of calcium. I have a spreadsheet that can calculate all of this even with "ideal" maximum precipitation to get to saturation of calcium carbonate.

For these calculations, I'll use Cal-Hypo 65% added to 1 liter of water with a pH of 7.7, TA of 80 ppm, initial CH of 30 ppm. If you were to dissolve 30 grams in that liter then the most calcium carbonate that would precipitate would be only 0.169 grams. More would precipitate if you had higher alkalinity water, but still not that much more. The tests in the link you gave were in 1 liter graduated cylinders with 6.35 cm diameter so 1 liter is a height of 1000 cm^3 / (3.14159 * (6.35/2)^2) = 31.58 cm tall (they said it was 29 cm so this is about right). Look at their Figure 1 that shows that for a 30 g/L solution the precipitated height is 1.55 cm so a volume of 1.55 * 3.14159 * (6.35/2)^2 = 49.09 cm^3 and they said that this was 1.93 grams of precipitate so this was very low density (i.e. a fluffy precipitate). The fact that they are precipitating so much precipitate means that they must be using much higher alkalinity water for their experiments since to get 1.93 grams of calcium carbonate you would have to have nearly 1000 ppm Total Alkalinity water or that their calcium hypochlorite was not fully dissolving in the first place (which won't help you). And even if you did get 1.93 grams of calcium carbonate out of 30 grams of calcium hypochlorite (which I do not believe is possible at normal tap water alkalinity), that only reduces the calcium content by 1.93*(40.078/100.0869) / 30*(40.078/142.98) = 9.2%

So go ahead and do whatever you want, but I think it's pointless since you won't be able to precipitate out nearly enough calcium to prevent a rise in Calcium Hardness (CH) using the Cal-Hypo.

As for sources of chlorinating liquid in New Zealand, can't you use any of the following?

Clorogene Supplies 15% Available Chlorine

Liqua Chlor

Bluewater Liquid Pool Chlorine

CW Pool Liquid Chlorine

Poolstar Liquid Chlorine

Clark Liquid Chlorine

Pool Doctor Liquid Chlorine

pool wise Liquid Chlorine

[jakenz]

Thanks Chem Geek, very informative as usual and exactly what i wanted to know.

Yes i am using liquid chlorine, with great success, only issue i have it salt levels building up quite quickly as my background chlorine usage is around 5ppm, not sure why it is this high, could be due to an old cover.