Why Use Bleach When It's So Expensive Compared To Cal Hypo?

[Dick]

I've seen many posts advocating use of regular grocery store bleach in lieu of pool store chlorine to save money. However, when I ran an analysis comparing the two, it looks like bleach is 51% to 71% more expensive and a LOT more cumbersome.

I have an outdoor 23,300 gal pool near a lot of trees (including !$#@%& cottonwoods) that's only open 4 months a year (5/15/ to maybe 9/15). During those 4 months I will go through one 100 lb pail of granular chlorine (calcium hypochlorite). Since cal hypo has 65% available chlorine that means I go through 65 lb of actual chlorine a season. If liquid bleach has 5% available chlorine (assuming for the sake of simplicity that is hasn't degraded), that means I would have had to buy 217 bottles of bleach [65 lb/((96 oz/bottle/16 oz/lb)(.05))] to get the same amount of available chlorine.

poolandspa.com sells 100 lb of cal hypo for $228.42 delivered to your door in two 50 lb pails (no I don't work for them I just found them with a quick Google search). The local Cub Foods carries three brands of bleach each in 96 oz bottles: their own brand @$1.66, Hilex Ultra @ $1.69 and Chlorox @ $1.81. 217 bottles would then cost $360, $367, and $408 and be 51%, 53% and 71% more expensive than cal hypo respectively. Also assuming a constant usage rate means buying and carting 12 bottles of bleach (weighing 72 lb) home every week for my 18-week season. So I'd have to spend 51% to 71% more and lug an additional 1202 lb of bleach home from the store. I realize that liquid chlorine has a definite advantage in some specific cases like opening a pool when the water is Kelly green or after a BIG party when you need to clean out a lot of bacteria but unless I'm missing something, this does not look like the best alternative for general sanitation. Again, am I missing something?

[chem geek]

I posted a comparison of the cost of chlorine sources at this link. Now the cost of chlorine varies by where you get it, but you will notice that the 12.5% chlorinating liquid was only $2.50 so would be equivalent to a 6% 96 ounce bottle of bleach (the Ultra and the Chlorox are 6%) for 99 cents. So for the prices of bleach you have found, they are not very economical. Most people find bleach at Costco for about $1 or sometimes a little more.

The main downside to using Cal-Hypo is that it increases the amount of Calcium Hardness (CH) in the pool by 0.7 ppm for every 1 ppm FC you add. This isn't terrible as regular dilution through backwashing or winter rains can take care of this increase or you can manually drain/refill if needed. Adding 100 ppm to CH over a year is not a problem the way that adding 100 ppm to CYA would be (if using Trichlor, for example). In your 23,300 gallon pool, adding 100 pounds of Cal-Hypo 65% is cumulatively 332 pm FC (that gets used up) and raises the CH by 234 ppm. Adjusting all other water parameters (i.e. keeping pH and TA the same) your calcium carbonate saturation index only increases by 0.2 assuming you started with 300 ppm CH. So only after several years would you have the potential problem of scaling and this assumes no splash-out, backwash, or drain/refill.

And unlike liquid forms of chlorine, the Cal-Hypo also comes in compressed slow-dissolving tablets, though I understand they don't dissolve as slowly or as well as Trichlor, but still, that's better than bleach that you have to add every single day (if you don't have a pool cover).

So yes, you can use Cal-Hypo and just watch your CH levels. I agree with you completely on that point. For my pool, the chlorinating liquid is convenient, not too expensive, and the plastic jugs are reused (I pay a deposit for each jug and for the case of 4 it comes in, but after the initial purchase, I just exchange an empty jug for a filled one and at the end of the season turn in the jugs and case for a credit). My pool is only 16,000 gallons and has an opaque automatic pool cover so my chlorine usage is rather low at around 0.5-0.7 ppm FC per day (about a cup to a cup and a half per day, though I just add it twice a week). To each his own!