Pre-dissolving Calcium Hypochlorite for use in Spa - good or bad idea?

SingingSailor

LifeTime Supporter
Aug 14, 2008
34
Trollhättan, Sweden
I'm just about to start with a small Spa, and will probably use a combination of dichlor and calcium hypo.
Can't use natrium hypo cause it's not economically available in Sweden except in too large quantities for a spa.

With a spa I understand I need to add chlorine pretty much daily, or at least everytime we use it. That's easy enough with quickly dissolving dichlor, but that alone will build-up cya too quickly. I have very soft water, so calcium hypo will work well, but the procedure of dissolving it in a bucket every day isn't tempting.

Thinking about pre-dissolving some calc hypo in a 2 liter bottle, maybe to a chlorine concentration similar to 5% bleach. I could then easily use a small amount of this liquid daily, having enough in the bottle for 2-4 weeks usage maybe.

Any dangers with this idea, e.g. is dissolved calc hypo stable in such concentration, or other drawbacks?
 

5tan

Active member
Jan 9, 2021
44
Canada
Pool Size
1643
Chlorine
Liquid Chlorine
While not quite the same, Calcium Increaser is an exothermic reaction when dissolved in water. 10-20 grams in a 500mL glass jar will get very hot, very quickly - I tested. If the instructions say do not pre-dissolve, I'd follow the instructions - it's likely because an exothermic reaction will take place. I'm sure we all remember pure sodium/calcium/potassium hitting water in high school chemistry, right?
 

SingingSailor

LifeTime Supporter
Aug 14, 2008
34
Trollhättan, Sweden
Thank's for answering guys!
I don't know about dissolving in advance, but I am curious why you wouldn't just use bleach (sodium hypochloride)?
Sorry, I made a translation error, with "Natrium hypo" I meant sodium hypochlorite. It would be rather expensive in Sweden for spas compared to Calcium hypochlorite.

While not quite the same, Calcium Increaser is an exothermic reaction when dissolved in water. 10-20 grams in a 500mL glass jar will get very hot, very quickly - I tested. If the instructions say do not pre-dissolve, I'd follow the instructions - it's likely because an exothermic reaction will take place. I'm sure we all remember pure sodium/calcium/potassium hitting water in high school chemistry, right?
Calcium increaser = Calcium Chloride, CaCl2. I think this gives more of an exothermic reaction with water than Calcium Hypochlorite. (In Sweden we also use Calcium Chloride to absorb moisture, e.g. in boats, because of its ability to attract water).
Instructions on the bottle of Calcium Hypochlorite actually says "dissolve in a bucket of water before pooring into the pool", which is what I have been doing all the time when I had the pool.
So my concerns are not so much about pre-dissolving it but more linked to the idea of keeping such solution stored for a couple of weeks, e.g. will it be stable? Or are there any other problems I haven't thought of.

I'm maybe a bit too precautious, but Calcium Hypochlorite can cause both explosions and Chlorine gas if not handled correctly, on top of being quite awkward to get on your skin or clothes, so better to ask you guys first :)
 
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