Water Softener Sizing Check

rlembkeFebruary 27, 2013

Hi guys -

Long time lurker, searcher and student of the many helpful folks here in the plumbing forum. Thank you all for your great contributions.

I'm finishing our home's basement and while doing the plumbing I want to add a water softener. I have heard great things about twin tank units and would prefer one if the numbers work. Currently looking at the Fleck 9100SXT with 2 x 1cf.

- 5 bed/4 bath w/ jacuzzi tub (rarely used)
- 2 adults, 2 kids, occasional family guests
- 2 dishwashers, washing machine
- SFR of 9gpm (measured at jacuzzi)
- 3/4" service
- irrigation will be with untreated water
- city water (all levels from 2012 report)
- hardness total = 188ppm max
- iron = n/a
- manganese = n/a
- pH = 9.1 - 9.8
- Alkalinity = 85ppm max
- TDS = 412ppm max
- Sulfates = 216ppm max
- Chloride = 100ppm max

The water here isn't terribly hard but every time I visit family with a Kinetico system, I dream of soft water. The usual white or green buildup on every faucet is getting old also.

Planning to do this DIY. I'm a mechanical engineer and I appreciate knowing things are done the right way while being smart with the $$.

I've been looking at Ohio Pure Water and have noted many of the usual items I need to request (Noryl bypass, top basket, gravel underbed, Purolite resin).

Thank you so very much for sharing your knowledge with the rest of us faceless lurkers!


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How low can you go on the salt dosage with a 1.0cf tank? 4lbs/cf would give a 16000 capacity, correct? Even at that capacity, I'm still looking at 10 days per regen per tank, right?

4 people x 75 gallons x 11 grains = 3300 grains/day
3300/16000 = 4.8 days/regen = ~10 days/regen each tank

I imagine as with most things, when you are working near the min or max of efficiency in one area, you're losing efficiency elsewhere.

    Bookmark   February 28, 2013 at 3:44PM
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You could go with a twin tank system at 1 cuft each, but I am curious as to why you want a twin tank system. Do you use water 24/7? :Unless you do, it is not likely worth the extra expense. Particularly when you have a jacuzzi tub, you would be better offer getting a single, slightly larger softener so you can get more flow to your tub without hardness bleed.

75 gallons per day per person is a bit high. Is this metered or a guess on your part? Generally 60 gallons per person per day is closer.

Your pH is crazy high, particularly for city water where they should be sending out water closer to neutral pH. I always recommend homeowners have the water in their homes tested because water can pick up a few things on its way from the city. In your case, this is not just recommended, it is absolutely necessary because of the high pH water. You need: TDS, pH, iron, manganese, hardness, alkalinity, chlorine (or chloramines - ask you city which you should expect to see), copper (not something we normally check for, but the high pH dictates).

Capacity: At 4 lb salt per cuft, you should see around 18,000 grains per cuft capacity. The tradeoff for lower salt dosage is more hardness bleed and more frequent regeneration. It also places your softener pretty close to minimum dosage, so is not generally something I recommend. The sweet spot between salt efficiency and water efficiency, while maintaining good softener operation is at 6 lb salt per cuft of resin.

This post was edited by aliceinwonderland_id on Fri, Mar 1, 13 at 15:51

    Bookmark   March 1, 2013 at 2:33PM
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Alice -

As I spend more and more time 'checking' my logic and math by looking at previous homeowners' requests for assistance, I think I realized the twin tank option just isn't a good one even before you confirmed it. Let's lay that option to bed.

I've also seen the 60 gal/person number used more often and started recalculating based on that. I haven't checked our actual usage but I will check that tonight. But using 60gal/person as a starting point, that puts my target 7-day regen needed capacity at 18500g (assuming the pH doesn't factor in). I'm guessing you're saying my SFR should be higher than just the demand of the jacuzzi. How much larger of a unit would you recommend to handle my SFR?

Here is a link to our utility's water report:


Regarding the pH, I was a little startled to see that high of a number as well. The report lists federal guidelines of 8.5 but then show they are trying to achieve >9.0. Is the pH something we should deal with?

Any recommendation for places to do water testing? I'll start looking locally in the meantime.

    Bookmark   March 1, 2013 at 5:12PM
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This test looks like it will check everything I need. Any other recommended labs?


The water district says it uses chloramines to disinfect - will chloride testing detect that?


    Bookmark   March 1, 2013 at 5:39PM
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Actual winter water usage has averaged around 140 gal/day over the past few years. Our two sons are only 7 and 4 so that will increase in coming years.

    Bookmark   March 1, 2013 at 7:15PM
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The test you linked looks fine.

Chloride testing will not detect chloramines. You can get that information from the city - if anything, chloramines will decrease a bit on the way to your home.

    Bookmark   March 4, 2013 at 10:00AM
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Found another lab that was well respected on a home brewing forum, very reasonable and in the Midwest. Samples sent off this morning so I should have results by week's end.

The water district's quality report lists chloramines as 1.4-4.3ppm, average of 3.0ppm.

    Bookmark   March 4, 2013 at 12:05PM
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Water test results back from Ward Labs

pH 9.5
TDS 388
Cations/Anions 6.2 / 6.7
Sodium 75 ppm
Potassium 7 ppm
Calcium 28 ppm
Magnesium 17 ppm
Total Hardness 141 ppm
Nitrate 0.6 ppm
Sulfate 53 ppm
Chloride 56 ppm
Carbonate 20 ppm
Bicarbonate 68 ppm
Total Alkalinity 89 ppm
Fluoride 0.61 ppm
Total Iron Manganese Copper Thoughts?

    Bookmark   March 7, 2013 at 7:57PM
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Your hardness is relatively low, which would place you at a 1.0 cuft softener. However, with your jacuzzi at 9 gpm you should go with a 1.5 cuft softener to ensure adequate softening for your flow rate.

I am a bit concerned with your pH. If I were you, I would get some test strips and check pH periodically. Most resins will operate up to the 9.5 - 10 pH range, placing you pretty close to max. Just monitor it for now.

When you look for your softener, you want the following:

1) 1.5 cuft softener
2) High quality American or German resin (better size distribution), standard mesh
3) 10% crosslinked resin. This will be more expensive, but the extra crosslinking will make the resin more resistant in the oxidizing environment of city water.
4) top distribution basket
5) gravel underbed
6) valve with metered control, such as Fleck 5600sxt or equivalent Clack valve
7) noryl bypass
8) plumb the softener in with a bypass so that it can be blocked in without disrupting water flow to your home
9) BLFC (brine line flow control) 0.5 gpm or smaller. This is not typically an issue, but it's a good idea to verify.

    Bookmark   March 8, 2013 at 11:08AM
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Thanks again for the advice, Alice.

How concerned should I be about the high pH? It seems pretty obvious to me that most of the deposits we see are due to the high pH and not necessarily our not-very hard water. What options are there for treating high pH - both whole-home and drinking water? I'm a little worried about what happens if I monitor the water and I reach that 10 or higher level.

So a 1.5 cuft unit, dosed at 9 lbs/regen will give a capacity of around 30000g, right? But I only need 18500g over a 7 day period. I'm curious what you'd recommend for the efficient settings, including regen time. If I didn't worry about the jacuzzi SFR, would I need to be concerned with SFR due to the number of bathrooms anyway?

    Bookmark   March 8, 2013 at 5:00PM
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Alice - any other comments? Anyone one else have any input to add?

I'm curious about the final settings for regen.

What are options for addressing high pH? I'm not finding much in this area.

I see the Purolite SST-60 resin says it operates in all pH levels. That's the only US 10% resin I see from OPWC - is that the one to pick?



    Bookmark   March 10, 2013 at 9:57PM
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A 1.5 cuft softener regenerating at 9# salt per cubic ft would give you a capacity of 38,000. However, there is no need for you to regen with 9# since you do not have iron in your water. The sweet spot between water efficiency and salt efficiency is at 6# salt/cuft resin, which would place you at 31,000 capacity. We could regen yours as low as 4#salt/cuft resin, for a capacity of 27,000

I you don't mind hardness leakage when filling the jacuzzi tub, you could go as low as 1.25 cuft, but I wouldn't go any lower for the fixtures in your home.

pH: A chemical injection system, consisting of a tank, controller, and chemical feed pump will take care of the problem. Either acetic acid or citric acid with alum will work. Some systems use sulfuric or hydrochloric acid but those are much more aggressive acids and typically used if water pH is 11 or higher.

Resin: SST-60, while a very good resin, is overkill for you. Yes, it has great chemical resistance capabilities, but it is also neutral-core resin, most suitable for iron-laden waters and much more expensive than other resins. There are other 10% crosslinked resins and other companies from which to purchase a softener. Just to name a few resins: Purolite c100x10, Dow HGR, Rohm and Haas IR-122

    Bookmark   March 12, 2013 at 11:02AM
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1.5 cuft Fleck 5600SXT unit ordered, delivered and installed! I walked through the manual regen process as has been outlined before to make sure the resin is rinsed well and backwash is clear, brine draw and fill all working properly.

Here are my first stabs at the settings. Let me know if I've missed any:

VT - Df1b
CT - Fd
NT - 1
C - 27
H - 11
SF - 20
DO - 10 (?)
RT - 2:00
BW - 10
BD - 60
RR - 10
BF - 4

BLFC is 0.5 so the BF is set to regen with #4/cuft or #6 total.

Am I ready to roll? Thank you again for your help! Can't wait to feel the new water!

    Bookmark   March 25, 2013 at 3:36PM
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Alice -

Just need a quick review, please. Thanks!

    Bookmark   March 27, 2013 at 1:21PM
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I was vacationing with no phone/internet access so did not see your post until this morning.

You settings look good.

    Bookmark   April 1, 2013 at 12:21PM
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Thanks Alice! My family and I are grateful for your advice and council.

God Bless

    Bookmark   April 2, 2013 at 7:49AM
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