Water softener setting

I've recently had a water softener put in, and I'm looking to configure it for the most efficient salt usage with an appropriate regeneration time.
The softener itself is the equivalent of a white-box computer. It was sold as a unit (by CAI Technologies), but I could have achieved the same result just by ordering parts separately, if I were more comfortable with my knowledge of the technology involved.
The control head is an Autotrol 762/255. The resin tank contains 1.5 ft^3 of Sybron Ionac C-249 cation resin.
I am using KCl instead of NaCl, for a few reasons.
My water hardness was measured by the softener retailer as 16gpg from a sample I sent. The latest quality report from my water company shows hardness as ranging from 105 to 339 ppm (~6-20gpg). I find it a bit strange that it varies so much, since the water comes from a single well that's right at the corner of my property. For now, I'm assuming that it stays at the high end, but will be doing some periodic testing to make sure.
Right now, I have the control head set at 16gpg, with the factory default of 9lb/ft^3 of salt and subsequently calculated 43K grains of softening capacity (using its built-in salt table which says 9lb/ft^3 has a capacity of 28673 grains/ft^3).
I've downloaded the data sheet for Ionac C-249, and they have a capacity chart which seems to show 25000 grains/ft^3 at 9lb/ft^3 of salt with 20gpg water. The line seems to cross 20000 grains/ft^3 at 6lb/ft^3 of salt.
Assuming 200 gallons of usage per day (which is a bit more than what we average), I calculate these results:
6lb/ft^3 salt, 30K grains = 9 days between regeneration (41/year), 9 lb KCl per regeneration (369 lb/year)
9lb/ft^3 salt, 37.5K grains = 11 days between regeneration (34/year), 13.5 lb KCl per regeneration (459 lb/year)
That's more than two 40lb bags of KCl (at $9.47 each), versus around 400 gallons more water used in a year (at about $0.01/gallon).
Can anyone with a bit of experience with water softeners give me a sanity check on those numbers? Is there a better source for grain capacity on this resin than a low-resolution chart?
For that matter, is there any difference in resin capacity between Na and K ions?
--
- Mike

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Mike Ruskai wrote:

hardness in their appliance center if they sell water softeners there.
--

Bill
In Hamptonburgh, NY
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wrote:

Thats a lot of calculating for a water softener! I simply entered the water hardness a bit higher then what was reported by the water company. To find the most economical setting I very slowly lowered the setting ove a period of a few weeks until I could feel that the softner couldn't keep up. Then I bumped it up a bit and I was done.
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There is a calculator which you may use to check your calculations at --
http://www.qualitywaterassociates.com/sizing.php
If you use KCl rather than NaCl, the salt dosage should be increased about 27% at each recharge.
SJF
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On or about Thu, 10 May 2007 00:14:04 -0700 did "SJF"

This calculator exactly matches my results for 6lb/ft^3 of salt, so that helps.

That seems a bit much. I'll try to verify that number, but at least it's something to go on.
Thanks.
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- Mike

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OK Mike. I had to buy a new unit (Fleck 5600) a year ago and went through all the calculations. Tedious, and the question comes up as to achieving the best efficiency consistent with convenience. There are tradeoffs and the different annual cost of salt turned out to be not very significant to me as one approached the highest efficiency settings. I do not use KCl which would magnify the difference, of course.
For any operating cycle, there is generally one day at the end of the cycle that results in a loss of usable capacity. Particularly, if you have a water supply of varying hardness, the margin for error must be set liberally. This affects the overall efficiency and suggests that the problem can be reduced by going to less frequent recharges. So there are countervailing forces working on the efficiency. I expect that if you have a low salt recharge that would normally run less than a week, you have lost any efficiency that might be achieved by a short cycle. I settled on something a bit above what is sometimes considered optimum. Good solution for me. In California, there is a lot of concern about environmental factors -- return of salt to groundwater -- and there are local regulations aiming a the salt efficient settings. Sometimes, these things go a bit far.
On the KCl vs. NaCl thing --
I took the number from an unremembered source I considered probably reliable. Checking, I find that the molecular weight of KCl is 27% greater than that of NaCl so you would need the extra weight of salt to provide an equivalent recharge. Since the solubility of KCl at 20 degrees Centigrade is essentially the same as for NaCl, the water used for brining would need to be increased 27% to get the extra salt.
For a long retired, and pretty rusty engineer, this exploration into water softener technology was a pretty interesting exercise -- another where a perfect answer is not in the cards. As Yogi Berra said, "If you come to a fork in the road, take it."
SJF
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Mike, you need to study the sizing page info and then plug your data into my calculator. You don't want to go more than 7-9 days between regenerations, its not good for resin.
SJF, there are two parts to correctly sizing a softener; salt dose capacity and the SFR gpm of the volume of resin which allows the softener to be able to remove all the hardness in the water as long as the peak demand gpm is never greater than the SFR gpm.
Everyone, all softening resin is made in the sodium form, none is made in the postassium form. All softenrs can use either potassium or sodium chloride. Softeners only use the sodium or potassium, none of the chloride. Potassium is not as efficient as sodium, I do not know why, it simply is, so you must use more potassium than salt unless you are using a high salt dose. I.E. for 6 lb/cuft (3333 grains/lb), you must increase by 12% (per the manufacturer).
I size softeners for much greater salt efficiency (and thereby water use efficiency also) than 6 lbs/cuft and experience says 27-30% higher salt dose if you are going to use potassium chloride. That and getting the SFR gpm correct, allows my softeners to remove all the hardness (produce 0 gpg soft water) between regenerations as long as your peak demand is never higher than the SFR gpm of the volume of resin in the tank.
To see how much sodium is added to softened water; the formula is 7.85 mg/l (roughly a quart) per gpg of ion exchange. I.E. 25 gpg * 7.85 181 mg of soddium added to roughly a quart of your softened water.
If you look at a loaf of white bread, you'll usually see 120-160 mg of sodium per slice. An 8 oz glass of skim milk, 530 mg. V8 juice, 560 mg. So unless you have much harder water or you are under a low sodium or sodium restricted diet, there is little to worry about and IF you are, you kow how to count your sodium intake and adjust it to your numbers.
IMO, based on 20+ years in selling and servicing softeners etc., I suggest using solar crystal sodium chloride and reducing sodium intake by reading food and beverage labels. That includes well, bottled and city waters, all contain some sodium naturally.
Gary Quality Water Associates
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On or about 12 May 2007 11:24:18 -0700 did Gary Slusser

Thanks for the information, but as I said in the original message, I chose KCl for a variety of reasons. That was my shorthand way of saying it was not just to avoid drinking extra sodium in the water.
A couple of the other reasons:
1) Potassium helps plants given softened water, while sodium harms them. I'm not just talking about house plants, either.
2) Potassium is neutral to the bacteria in my septic tank, while sodium *may* harm them. There's next to no reliable information on how anaerobic septic systems deal with sodium-softened water, but some anecdotal claims from those cleaning out septic systems correlate reduced solids breakdown with the use of sodium ion exchange water softeners.
3) The addition of potassium to our drinking water is a dietary benefit.
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"Gary Slusser" >

Gary, do you have a retail website? What do you need to know to properly "size" a softener? I am about ready to buy... replacing a leased culligan : / Thanks
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On or about Thu, 10 May 2007 15:09:52 -0700 did "SJF"

This is how I should have approached the question. It's been a while since my last chemistry class, where that mode of thinking would have been natural.
Now, if only I knew what temperature the softener assumed for calculating the quantity of water to push back into the brine tank.
I'll probably be safe going with 8lb/ft^3 instead of 6lb (at the same 30K grain capacity), which more than compensates for the molecular weight difference, and thus leaves a bit of a buffer for the temperature being lower than the softener may expect.
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Mike,
I'm not sure why you are going through all of these calculations. If you set the regeneration time too long you will quickly realize that there is a problem and do a "manual regeneration" thus throwing all of your calculations out the window. Your water supply apparently has a variable hardness so set the regeneration time assuming the highest hardness and your water will always be soft. If you try to be super efficient about regenerating you will certainly fail because the actual water hardness varies. Set it and forget it. I'm pretty sure that you need a "fudge" factor when you substitute KCl for NaCl.
Dave M.
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On or about Thu, 10 May 2007 13:08:15 GMT did "David Martel"

As I specified in the beginning, I have an Autotrol 762/255 head. That's a metering control head, so I don't set the regeneration time.
I was calculating salt usage. Resin has a variable capacity based on how much brine you flush through it, and it's not linear. Using 9 pounds nets you 30K grains of softening capacity. Using 13.5 pounds doesn't net you 13.5/9*30 = 45K, but only 37.5K grains.
So using less salt and regenerating more often uses, over time, less total salt and more water (more regeneration).
I was looking for someone to verify that my numbers were correct, but it seems I aimed a bit over most people's heads.
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- Mike

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