Chlorine Usage Calculations

#1
I’m considering switching from the trichlor hockey pucks to liquid chlorine. I wanted to get a feel for how much bleach or pool store liquid chlorine I’d need. So I did a chlorine usage calculation for the trichlor pucks. I purchased the pucks on Aug. 5, 2010. I assumed I started using those pucks two weeks after I bought them. I also know when I’ve opened and closed the pool since then. It turns out that I’ve used 35 pounds of pucks across a span of 30 weeks. That works out to be just 2.67 ozs/day for a 22,500 gallon pool in Massachusetts that gets full sun from about 8:00 AM until sunset. When I stop to think about it that doesn’t sound like much chlorine. :p We do have a mineral sanitizer cartridge as part of our pool equipment so I run lower chlorine levels. And as I recall last summer I needed to shock the pool two or three times because of cloudiness/beginning algae. So this year I’ve been running a higher chlorine level (1.5 ppm or so). The pucks weigh 8 ounces each so I’ve been using just one third of a puck per day. The bather load is light and does not include dogs or kids.

Using the Pool Calculator on this forum I calculate that 2.67 ozs of trichlor is equivalent to 43 ounces of 5.25% bleach or 18 ounces of 12.5% liquid chlorine. So I’d be looking at adding a quart and third of bleach per day, or a little over a pint of the liquid pool shock. Does this seem reasonable? I realize these are average values. I plan to dose more when we have very sunny days and dose less when it’s cloudy.
 

topher

Well-known member
Jun 24, 2012
136
toronto, Ontario, Canada
#2
dont forget about the CYA that the pucks also put into the water wich will eventually require you to use more and more chlorine.
this is my first year using liquid only and so far my pool has NEVER been clearer than it is now. I still require borax and salt in my pool but I am now getting all my levels correct first before I play with the extra additives.
 

duraleigh

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#3
You'll probably use more than that in a 22.5k pool. Without doing the math, anecdotal reports on the forum indicate a 22k pool might use around .5 to .75 gallons of 6% Clorox.

If you switch, don't do it to save money (although you might). Switch because you understand the deficiencies of chlorinating with tri-chlor. If your pool is and has been running just fine with tri-chlor pucks, don't switch at all.
 
#4
topher

Why do you add salt to your pool if you're using liquid chlorine? If you don't have a salt water generator what is the reason for adding salt?

duraleigh

Two reasons for switching to liquid chlorine. First, I'm getting tired of constantly adding TA up and pH down as a result of using trichlor. Second, my CYA levels are creeping up. They're at 65 ppm now. Our pool gets over 12 hours of direct sun per day so I don't have a problem with CYA being somewhat above the 30 - 50 ppm recommended range. But I really don't want it going much higher than it is now. So for the rest of this pool season I plan to use liquid chlorine.
 

Swampwoman

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Apr 27, 2012
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Grand Rapids, MI
#6
My pool is 22,000 gallons and I use a jug of bleach a day on average, which equates to 2 ppm. Sometimes 3 ppm. I am in partial sun daily, with about 30 percent shaded. But I target 4-7 ppm in accordance with the cya/chlorine chart for adequate preventative sanitation.
People regularly comment that my water seems so clear and sparkly. It does not smell of chlorine (no ccs) and feels silky on the skin (I added 50 ppm of borates). I buy my 6% chlorine at aldi's for $1.19.

If you were trying to keep the same free chlorine that I am, you'd be using more pucks. The recommended FC is driven by the science that shows how stabilizer interferes with the disinfecting capability of chlorine, coupled with the science that show chloramines (ccs) have negative health consequences.

These are the reasons -- not necessarily fiscal -- to use the BBB method to my mind. What it means is that you need to test FC and ph daily, and will likely have to add muriatic acid about every 10 days or so to keep the ph in range. (bleach tends to raise ph a little, pucks tend to lower.)
All of this only actually takes a few minutes of routine daily maintenance.

In the daily sense, it's not more convenient than pucks, but in the preventativ sense, it saves time and money by ensuring algae does not ever get a foothold.

So if the hassle of adding ph up bugs you with pucks, don't expect bbb to be simpler or necessarily cheaper. But if you want to ensure that you have absolutey beautiful water and that you don't end up with chlorine lock, I suspect you'd be well served by the bbb approach. It's not so much what you put in in terms of product as it
is a method wherein testing and expected outcomes based on knowledgeable management form the crux of the practice.